diff --git a/src/app/plugins/locales/en.json b/src/app/plugins/locales/en.json
index 2232d0408..ac816526b 100644
--- a/src/app/plugins/locales/en.json
+++ b/src/app/plugins/locales/en.json
@@ -102,7 +102,7 @@
     "cancel": "Cancel",
     "proceed": "proceed",
     "confirm": "Confirm",
-    "delete":"Delete",
+    "delete": "Delete",
     "add": "Add",
     "text": "Text",
     "value": "Value",
@@ -300,7 +300,27 @@
   },
   "cooperators": {
     "updatedRole": "Updated role to {role} for: {users}",
-    "inviteSent": "Invitation sent to: {users}"
+    "inviteSent": "Invitation sent to: {users}",
+    "validation": {
+      "invalidEmail": "Please enter a valid email address.",
+      "invalidFormat": "Please enter a valid email address.",
+      "inviteSelf": "You cannot invite yourself.",
+      "inviteOwner": "The study owner cannot be invited as a cooperator.",
+      "alreadyCooperator": "This email is already a cooperator for this study."
+    },
+    "invite": {
+      "title": "Send Invitation",
+      "emailPlaceholder": "Type cooperator email",
+      "emailInputPlaceholder": "Type an email address",
+      "role": "Role",
+      "date": "Date",
+      "time": "Time",
+      "message": "Invitation Message",
+      "messagePlaceholder": "Enter your invitation message",
+      "cancel": "Cancel",
+      "send": "Send",
+      "alreadySelected": "{email} has already been selected"
+    }
   },
   "navigation": {
     "dashboard": "Dashboard",
@@ -981,12 +1001,48 @@
   },
   "UsabilityCooperators": {
     "inviteEvaluator": "Invite Evaluator To Test",
+    "inviteEvaluatorDescription": "Send evaluation invitations to participants",
     "email": "Email",
     "scheduledAt": "Scheduled at",
     "inviteMessage": "Invite message",
+    "inviteMessageDescription": "Write a personalized message to include with the invitation.",
     "placeholderMessage": "Hey, let's make a test...",
     "inviteInfo": "Invite with test link will be sent to evaluator email at scheduled time",
-    "send": "Send"
+    "send": "Send",
+
+    "role": "Role",
+    "roleDescription": "Select the role for this participant.",
+
+    "roles": {
+      "evaluator": "Evaluator",
+      "evaluatorDesc": "Participates in the test, shares screen/video.",
+      "observator": "Observator",
+      "observatorDesc": "Watches the session silently, takes notes."
+    },
+
+    "selectParticipantDescription": "Select the participant you want to invite to this evaluation session.",
+    "emailPlaceholder": "Type an email address and press Enter",
+    "addedParticipants": "Added participants",
+    "noParticipantSelected": "No participant selected",
+
+    "scheduleDescription": "Choose the date and time for the evaluation session.",
+
+    "invitationPreview": "Invitation Preview",
+    "evaluationInvitation": "Evaluation Invitation",
+
+    "to": "To",
+    "scheduled": "Scheduled",
+    "message": "Message",
+
+    "noMessageYet": "No message entered yet...",
+
+    "inviteInfoTitle": "Information",
+    "inviteInfoDescription": "The participant will receive an email notification and can accept or decline the invitation.",
+
+    "validation": {
+      "invalidEmail": "Invalid email: {email}",
+      "dateRequired": "Date is required"
+    }
   },
   "HeuristicsCooperators": {
     "title": {
diff --git a/src/app/plugins/locales/es.json b/src/app/plugins/locales/es.json
index a5b4885d8..2c8ad81ab 100644
--- a/src/app/plugins/locales/es.json
+++ b/src/app/plugins/locales/es.json
@@ -98,7 +98,7 @@
     "description": "Descripción",
     "cancel": "Cancelar",
     "confirm": "Confirmar",
-    "delete":"Eliminar",
+    "delete": "Eliminar",
     "add": "Agregar",
     "text": "Texto",
     "value": "Valor",
@@ -298,7 +298,27 @@
   },
   "cooperators": {
     "updatedRole": "Rol actualizado a {role} para: {users}",
-    "inviteSent": "Invitación enviada a: {users}"
+    "inviteSent": "Invitación enviada a: {users}",
+    "validation": {
+      "invalidEmail": "Por favor, introduce un correo electrónico válido.",
+      "invalidFormat": "Por favor, introduce un correo electrónico válido.",
+      "inviteSelf": "No puedes invitarte a ti mismo.",
+      "inviteOwner": "El propietario del estudio no puede ser invitado como colaborador.",
+      "alreadyCooperator": "Este correo ya es un colaborador de este estudio."
+    },
+    "invite": {
+      "title": "Enviar invitación",
+      "emailPlaceholder": "Correo del colaborador",
+      "emailInputPlaceholder": "Escribe un correo electrónico",
+      "role": "Rol",
+      "date": "Fecha",
+      "time": "Hora",
+      "message": "Mensaje de invitación",
+      "messagePlaceholder": "Escribe tu mensaje de invitación",
+      "cancel": "Cancelar",
+      "send": "Enviar",
+      "alreadySelected": "{email} ya fue seleccionado"
+    }
   },
   "navigation": {
     "dashboard": "Panel",
@@ -902,12 +922,48 @@
   },
   "UsabilityCooperators": {
     "inviteEvaluator": "Invitar evaluador a la prueba",
+    "inviteMessageDescription": "Escribe un mensaje personalizado para incluir en la invitación.",
+    "inviteEvaluatorDescription": "Envía invitaciones de evaluación a los participantes",
     "email": "Correo electrónico",
-    "scheduledAt": "Programado para",
+    "scheduledAt": "Programado en",
     "inviteMessage": "Mensaje de invitación",
     "placeholderMessage": "Hola, hagamos una prueba...",
-    "inviteInfo": "La invitación con el enlace de la prueba se enviará al correo del evaluador en el horario programado",
-    "send": "Enviar"
+    "inviteInfo": "La invitación con el enlace de la prueba será enviada al correo del evaluador en el horario programado",
+    "send": "Enviar",
+
+    "role": "Rol",
+    "roleDescription": "Selecciona el rol para este participante.",
+
+    "roles": {
+      "evaluator": "Evaluador",
+      "evaluatorDesc": "Participa en la prueba, comparte pantalla/video.",
+      "observator": "Observador",
+      "observatorDesc": "Observa la sesión en silencio y toma notas."
+    },
+
+    "selectParticipantDescription": "Selecciona el participante que deseas invitar a esta sesión de evaluación.",
+    "emailPlaceholder": "Escribe un correo electrónico y presiona Enter",
+    "addedParticipants": "Participantes añadidos",
+    "noParticipantSelected": "Ningún participante seleccionado",
+
+    "scheduleDescription": "Elige la fecha y hora de la sesión de evaluación.",
+
+    "invitationPreview": "Vista previa de la invitación",
+    "evaluationInvitation": "Invitación de evaluación",
+
+    "to": "Para",
+    "scheduled": "Programado",
+    "message": "Mensaje",
+
+    "noMessageYet": "Aún no se ha ingresado ningún mensaje...",
+
+    "inviteInfoTitle": "Información",
+    "inviteInfoDescription": "El participante recibirá una notificación por correo electrónico y podrá aceptar o rechazar la invitación.",
+
+    "validation": {
+      "invalidEmail": "Correo inválido: {email}",
+      "dateRequired": "La fecha es obligatoria"
+    }
   },
   "HeuristicsCooperators": {
     "title": {
diff --git a/src/shared/components/dialogs/InviteDialog.vue b/src/shared/components/dialogs/InviteDialog.vue
index 37dddb45a..56d3f096b 100644
--- a/src/shared/components/dialogs/InviteDialog.vue
+++ b/src/shared/components/dialogs/InviteDialog.vue
@@ -7,28 +7,29 @@
     <v-card class="rounded-lg">
       <v-card-title style="color: white" class="bg-primary rounded-top-lg">
         <v-icon color="white" class="mr-2"> mdi-account-plus </v-icon>
-        {{ title || 'Send Invitation' }}
+        {{ title || t('cooperators.invite.title') }}
       </v-card-title>
       <v-card-text class="pt-4">
-        <v-combobox
-          :key="comboboxKey"
-          ref="combobox"
-          v-model="comboboxModel"
-          :items="users.filter((user) => user?.email != null)"
-          item-title="email"
-          :label="selectLabel || 'Select cooperator'"
-          multiple
-          variant="outlined"
-          density="comfortable"
-          @update:model-value="validateEmail"
-        >
-          <template #no-data>
-            {{
-              noDataText ||
-              'There are no users registered with that email, press enter to select anyways.'
-            }}
-          </template>
-        </v-combobox>
+        <v-row class="ma-0">
+          <v-text-field
+            v-model="emailInput"
+            :label="selectLabel || t('cooperators.invite.emailPlaceholder')"
+            variant="outlined"
+            density="comfortable"
+            placeholder="Type an email address"
+            prepend-inner-icon="mdi-email-outline"
+            clearable
+            @keydown.enter.prevent="addEmailToSelection"
+          />
+          <v-btn
+            class="ml-2"
+            icon
+            variant="outlined"
+            :disabled="!emailInput.trim()"
+            @click="addEmailToSelection"
+            ><v-icon>mdi-plus</v-icon></v-btn
+          >
+        </v-row>
 
         <div class="d-flex flex-wrap mt-1">
           <v-chip
@@ -45,7 +46,7 @@
         <v-select
           v-model="selectedRole"
           :items="roleOptions"
-          :label="roleLabel || 'Role'"
+          :label="roleLabel || t('cooperators.invite.role')"
           variant="outlined"
           density="comfortable"
           class="mt-4"
@@ -68,7 +69,7 @@
                   v-bind="props"
                   variant="outlined"
                   density="compact"
-                  label="Date"
+                  :label="t('cooperators.invite.date')"
                   prepend-inner-icon="mdi-calendar"
                 />
               </template>
@@ -98,7 +99,7 @@
                   density="compact"
                   color="primary"
                   variant="outlined"
-                  label="Time"
+                  :label="t('cooperators.invite.time')"
                   readonly
                   v-bind="props"
                 />
@@ -118,8 +119,10 @@
           v-if="showInviteMessage"
           v-model="inviteMessage"
           color="primary"
-          :label="messageLabel || 'Invitation Message'"
-          :placeholder="messagePlaceholder || 'Enter your invitation message'"
+          :label="messageLabel || t('cooperators.invite.message')"
+          :placeholder="
+            messagePlaceholder || t('cooperators.invite.messagePlaceholder')
+          "
           variant="outlined"
           class="mt-4"
         />
@@ -135,7 +138,7 @@
           class="rounded-lg"
           @click="onCancel"
         >
-          {{ cancelText || 'Cancel' }}
+          {{ cancelText || t('cooperators.invite.cancel') }}
         </v-btn>
         <v-btn
           color="primary"
@@ -143,7 +146,7 @@
           :disabled="selectedCoops.length === 0"
           @click="onSend"
         >
-          {{ sendText || 'Send' }}
+          {{ sendText || t('cooperators.invite.send') }}
         </v-btn>
       </v-card-actions>
     </v-card>
@@ -152,8 +155,15 @@
 
 <script setup>
 import { ref, computed, watch } from 'vue'
-import { useCooperatorUtils } from '@/shared/composables/useCooperatorUtils'
+import {
+  useCooperatorUtils,
+  getCooperatorInviteValidationError,
+  normalizeCooperatorInviteEntry,
+} from '@/shared/composables/useCooperatorUtils'
 import { showError, showWarning } from '@/shared/utils/toast'
+import { useI18n } from 'vue-i18n'
+
+const { t } = useI18n()
 
 const props = defineProps({
   show: {
@@ -164,6 +174,18 @@ const props = defineProps({
     type: Array,
     default: () => [],
   },
+  existingCooperators: {
+    type: Array,
+    default: () => [],
+  },
+  currentUserEmail: {
+    type: String,
+    default: '',
+  },
+  studyOwnerEmail: {
+    type: String,
+    default: '',
+  },
   showDateTimeSelection: {
     type: Boolean,
     default: false,
@@ -186,15 +208,13 @@ const props = defineProps({
 const emit = defineEmits(['update:show', 'send-invitations'])
 
 // Use composables
-const { roleOptions, validateEmail: isValidEmail } = useCooperatorUtils()
+const { roleOptions } = useCooperatorUtils()
 
 // Local state
 const selectedCoops = ref([])
-const comboboxModel = ref([])
-const comboboxKey = ref(0)
 const selectedRole = ref(1)
 const inviteMessage = ref('')
-const combobox = ref(null)
+const emailInput = ref('')
 
 // Date and time for scheduling (accessibility tests)
 const date = ref(
@@ -231,53 +251,40 @@ const removeSelectedCoop = (index) => {
   selectedCoops.value.splice(index, 1)
 }
 
-const isStringEmail = (email) => {
-  return typeof email !== 'object' && email !== undefined && email.length > 0
-}
-
-const isUserEmailValid = (email) => {
-  return props.users.find((user) => user.email === email)
-}
-
 const isCoopAlreadySelected = (emailToCheck) => {
   return selectedCoops.value.find(
     (coop) => (typeof coop === 'object' ? coop.email : coop) === emailToCheck,
   )
 }
 
-const validateEmail = () => {
-  const email = comboboxModel.value.pop()
-  comboboxKey.value++
-
-  if (!email) return
-
-  // Handle string email input
-  if (isStringEmail(email)) {
-    if (!isValidEmail(email)) {
-      showError('Invalid email format')
-      return
-    }
-
-    if (!isUserEmailValid(email)) {
-      showError(`${email} is not a valid email or does not exist`)
-      return
-    }
-
-    if (!selectedCoops.value.includes(email)) {
-      selectedCoops.value.push(email)
-    }
+const addEmailToSelection = () => {
+  const rawValue = emailInput.value.trim()
+  if (!rawValue) return
+
+  const validationError = getCooperatorInviteValidationError({
+    email: rawValue,
+    currentUserEmail: props.currentUserEmail,
+    studyOwnerEmail: props.studyOwnerEmail,
+    existingCooperators: props.existingCooperators,
+    t,
+  })
+
+  if (validationError) {
+    showError(validationError)
+    emailInput.value = ''
     return
   }
 
-  // Handle object email input
-  if (selectedCoops.value.includes(email)) return
-
-  if (isCoopAlreadySelected(email.email)) {
-    showWarning(`${email.email} has already been selected`)
+  if (isCoopAlreadySelected(rawValue)) {
+    showWarning(t('cooperators.invite.alreadySelected', { email: rawValue }))
+    emailInput.value = ''
     return
   }
 
-  selectedCoops.value.push(email)
+  selectedCoops.value.push(
+    normalizeCooperatorInviteEntry(rawValue, props.users),
+  )
+  emailInput.value = ''
 }
 
 const onCancel = () => {
@@ -303,10 +310,9 @@ const onSend = () => {
 
 const resetForm = () => {
   selectedCoops.value = []
-  comboboxModel.value = []
   inviteMessage.value = ''
   selectedRole.value = 1
-  combobox.value?.blur()
+  emailInput.value = ''
 }
 
 // Watch for dialog visibility to reset form
@@ -334,6 +340,13 @@ watch(
   text-transform: unset !important;
 }
 
+:deep(.v-btn) {
+  border-radius: 12px;
+  text-transform: none;
+  font-weight: 600;
+  letter-spacing: 0.02em;
+}
+
 .email-chip {
   max-width: 100%;
 }
diff --git a/src/shared/composables/useCooperatorUtils.js b/src/shared/composables/useCooperatorUtils.js
index 977801679..83363408f 100644
--- a/src/shared/composables/useCooperatorUtils.js
+++ b/src/shared/composables/useCooperatorUtils.js
@@ -3,6 +3,81 @@ import { getStatusColor, getStatusText } from '@/shared/utils/statusUtils'
 import { formatDate, formatTime } from '@/shared/utils/dateUtils'
 import { formatInitials } from '@/shared/utils/formatUtils'
 
+export const normalizeCooperatorInviteEntry = (entry, registeredUsers = []) => {
+  if (!entry) {
+    return { email: '', userDocId: null }
+  }
+
+  if (typeof entry === 'string') {
+    const email = entry.trim()
+    const normalizedEmail = email.toLowerCase()
+    const matchedUser = registeredUsers.find((user) => {
+      return user?.email?.trim()?.toLowerCase() === normalizedEmail
+    })
+
+    return {
+      email,
+      userDocId: matchedUser?.id || matchedUser?.userDocId || null,
+    }
+  }
+
+  const email = entry?.email?.trim() || entry?.value?.trim() || ''
+  const matchedUser = registeredUsers.find((user) => {
+    return user?.email?.trim()?.toLowerCase() === email.trim().toLowerCase()
+  })
+
+  return {
+    email,
+    userDocId:
+      entry?.userDocId ||
+      entry?.id ||
+      matchedUser?.id ||
+      matchedUser?.userDocId ||
+      null,
+  }
+}
+
+export const getCooperatorInviteValidationError = ({
+  email,
+  currentUserEmail,
+  studyOwnerEmail,
+  existingCooperators = [],
+  t,
+}) => {
+  if (!email || typeof email !== 'string') {
+    return t('cooperators.validation.invalidEmail')
+  }
+
+  const normalizedEmail = email.trim().toLowerCase()
+  if (!normalizedEmail.includes('@') || !normalizedEmail.includes('.')) {
+    return t('cooperators.validation.invalidFormat')
+  }
+
+  if (
+    currentUserEmail &&
+    normalizedEmail === currentUserEmail.trim().toLowerCase()
+  ) {
+    return t('cooperators.validation.inviteSelf')
+  }
+
+  if (
+    studyOwnerEmail &&
+    normalizedEmail === studyOwnerEmail.trim().toLowerCase()
+  ) {
+    return t('cooperators.validation.inviteOwner')
+  }
+
+  const alreadyCooperator = existingCooperators.some((cooperator) => {
+    return cooperator?.email?.trim()?.toLowerCase() === normalizedEmail
+  })
+
+  if (alreadyCooperator) {
+    return t('cooperators.validation.alreadyCooperator')
+  }
+
+  return null
+}
+
 /**
  * Composable for common cooperator utilities
  */
@@ -74,5 +149,6 @@ export function useCooperatorUtils() {
     formatDate,
     formatTime,
     validateEmail,
+    getCooperatorInviteValidationError,
   }
 }
diff --git a/src/shared/views/CooperatorsView.vue b/src/shared/views/CooperatorsView.vue
index 6bae2a3a8..ea1392a83 100644
--- a/src/shared/views/CooperatorsView.vue
+++ b/src/shared/views/CooperatorsView.vue
@@ -64,7 +64,9 @@
     <!-- Invite Dialog -->
     <InviteDialog
       v-model:show="showInviteDialog"
-      :users="users"
+      :existing-cooperators="cooperatorsEdit"
+      :current-user-email="userAuth?.email"
+      :study-owner-email="test?.testAdmin?.email"
       :show-date-time-selection="false"
       :title="$t('HeuristicsCooperators.actions.send_invitation')"
       :select-label="$t('HeuristicsCooperators.actions.select_cooperator')"
@@ -72,6 +74,7 @@
       :role-label="$t('HeuristicsCooperators.headers.role')"
       :cancel-text="$t('HeuristicsCooperators.actions.cancel')"
       :send-text="$t('HeuristicsCooperators.actions.send')"
+      :users="cooperatorsEdit"
       @send-invitations="handleSendInvitations"
     />
 
@@ -115,7 +118,10 @@ import MessageDialog from '@/shared/components/dialogs/MessageDialog.vue'
 import InviteDialog from '@/shared/components/dialogs/InviteDialog.vue'
 import ConfirmDialog from '@/shared/components/dialogs/ConfirmDialog.vue'
 import UIDGenerator from 'uid-generator'
-import { useCooperatorUtils } from '@/shared/composables/useCooperatorUtils'
+import {
+  useCooperatorUtils,
+  normalizeCooperatorInviteEntry,
+} from '@/shared/composables/useCooperatorUtils'
 import { useCooperatorActions } from '@/shared/composables/useCooperatorActions'
 import Cooperators from '../models/Cooperators'
 import { getMethodManagerView } from '../constants/methodDefinitions'
@@ -154,7 +160,7 @@ const route = useRoute()
 const slots = useSlots()
 const { t } = useI18n()
 
-const { roleOptions } = useCooperatorUtils()
+const { roleOptions, getCooperatorInviteValidationError } = useCooperatorUtils()
 
 useCooperatorActions() // Keep the hook call in case it has side effects
 
@@ -276,7 +282,6 @@ const showIntroView = computed(() => {
 const dialog = computed(() => store.getters.getDialogLeaveStatus)
 const test = computed(() => store.getters.test)
 const userAuth = computed(() => store.getters.user)
-const users = computed(() => store.state.Users?.users || [])
 const cooperatorsEdit = computed(() =>
   test.value?.cooperators ? [...test.value.cooperators] : [],
 )
@@ -342,47 +347,45 @@ const handleSendInvitations = async (invitationData) => {
   cooperatorsUpdate.value = [...cooperatorsEdit.value]
 
   selectedCoops.forEach((coop) => {
-    const coopEmail = coop.email || coop // Handle both object and string formats
+    const normalizedEntry = normalizeCooperatorInviteEntry(coop)
+    const coopEmail =
+      normalizedEntry?.email || (typeof coop === 'object' ? coop.email : coop)
+    const normalizedEmail = coopEmail?.trim().toLowerCase()
+
+    const validationError = getCooperatorInviteValidationError({
+      email: normalizedEmail,
+      currentUserEmail: userAuth.value?.email,
+      studyOwnerEmail: test.value?.testAdmin?.email,
+      existingCooperators: cooperatorsEdit.value,
+      t,
+    })
+
+    if (validationError) {
+      showError(validationError)
+      return
+    }
 
-    // Check if this email already exists in cooperators list
     const existingIndex = cooperatorsEdit.value.findIndex(
-      (c) => c.email === coopEmail,
+      (c) => c.email?.trim().toLowerCase() === normalizedEmail,
     )
 
     if (existingIndex === -1) {
-      // New email - create new cooperator entry
       const token = uidgen.generateSync()
-      if (!coop.id) {
-        cooperatorsEdit.value.push({
-          userDocId: null,
-          email: coop,
-          invited: true,
-          accepted: false,
-          accessLevel: roleOptions.value[selectedRole].value,
-          inviteMessage: inviteMessage || null,
-          token,
-          progress: 0,
-          updateDate: test.value?.updateDate || new Date().toISOString(),
-          testAuthorEmail: test.value?.testAdmin?.email || '',
-        })
-      } else {
-        cooperatorsEdit.value.push({
-          userDocId: coop.id,
-          email: coop.email,
-          invited: true,
-          accepted: false,
-          accessLevel: roleOptions.value[selectedRole].value,
-          inviteMessage: inviteMessage || null,
-          token,
-          progress: 0,
-          updateDate: test.value?.updateDate || new Date().toISOString(),
-          testAuthorEmail: test.value?.testAdmin?.email || '',
-        })
-      }
-      tokens[coop.id || coop] = token
+      cooperatorsEdit.value.push({
+        userDocId: normalizedEntry?.userDocId || null,
+        email: coopEmail,
+        invited: true,
+        accepted: false,
+        accessLevel: roleOptions.value[selectedRole].value,
+        inviteMessage: inviteMessage || null,
+        token,
+        progress: 0,
+        updateDate: test.value?.updateDate || new Date().toISOString(),
+        testAuthorEmail: test.value?.testAdmin?.email || '',
+      })
+      tokens[normalizedEntry?.userDocId || coopEmail] = token
       newInvites.push(coopEmail)
     } else {
-      // Email already exists - update their role instead of creating duplicate
       const existing = cooperatorsEdit.value[existingIndex]
       const newRole = roleOptions.value[selectedRole].value
 
@@ -390,7 +393,6 @@ const handleSendInvitations = async (invitationData) => {
         existing.accessLevel !== newRole ||
         existing.inviteMessage !== inviteMessage
       ) {
-        // Update the existing entry's role
         cooperatorsEdit.value[existingIndex] = {
           ...existing,
           accessLevel: newRole,
@@ -399,8 +401,7 @@ const handleSendInvitations = async (invitationData) => {
         }
         updatedRoles.push(coopEmail)
       }
-      // Keep existing token so their invite link still works
-      tokens[coop.id || coop] = existing.token
+      tokens[normalizedEntry?.userDocId || coopEmail] = existing.token
     }
   })
 
@@ -668,7 +669,6 @@ const executeInvitationCancellation = async (guest) => {
 }
 
 const openDialog = async () => {
-  if (!store.state.Users?.users) store.dispatch('getAllUsers')
   if (slots.dialog) drawerOpen.value = true
   else showInviteDialog.value = true
 }
diff --git a/src/ux/UserTest/components/dialogs/CreateInviteDialog.vue b/src/ux/UserTest/components/dialogs/CreateInviteDialog.vue
index c6bf60d40..3092c86c2 100644
--- a/src/ux/UserTest/components/dialogs/CreateInviteDialog.vue
+++ b/src/ux/UserTest/components/dialogs/CreateInviteDialog.vue
@@ -16,7 +16,7 @@
             {{ $t('UsabilityCooperators.inviteEvaluator') }}
           </h2>
           <p class="text-body-2 mb-0 opacity-90">
-            Send evaluation invitations to participants
+            {{ $t('UsabilityCooperators.inviteEvaluatorDescription') }}
           </p>
         </div>
       </v-card-title>
@@ -32,10 +32,10 @@
                     <v-icon class="mr-2" size="20"
                       >mdi-account-cowboy-hat</v-icon
                     >
-                    Role
+                    {{ $t('UsabilityCooperators.role') }}
                   </label>
                   <p class="field-description mb-3">
-                    Select the role for this participant.
+                    {{ $t('UsabilityCooperators.roleDescription') }}
                   </p>
                   <v-radio-group
                     v-model="selectedRole"
@@ -65,102 +65,51 @@
                     <v-icon class="mr-2" size="20">mdi-account-outline</v-icon>
                     {{ $t('UsabilityCooperators.email') }}
                   </label>
+                  <p class="field-description mb-3"></p>
                   <p class="field-description mb-3">
-                    Select the participant you want to invite to this evaluation
-                    session.
+                    {{
+                      $t('UsabilityCooperators.selectParticipantDescription')
+                    }}
                   </p>
-                  <v-combobox
-                    ref="comboboxRef"
-                    v-model="comboboxModel"
-                    :items="filteredUsers"
-                    item-title="email"
-                    item-value="id"
-                    multiple
-                    chips
-                    variant="outlined"
-                    density="comfortable"
-                    placeholder="Type email address or select from list..."
-                    prepend-inner-icon="mdi-account-multiple-plus"
-                    color="primary"
-                    clearable
-                    :menu-props="{ maxHeight: 300 }"
-                    @update:model-value="validateEmailInput"
-                  >
-                    <template #chip="{ props, item }">
+                  <v-row class="ma-0">
+                    <v-text-field
+                      v-model="emailInput"
+                      variant="outlined"
+                      density="comfortable"
+                      :placeholder="$t('UsabilityCooperators.emailPlaceholder')"
+                      prepend-inner-icon="mdi-account-multiple-plus"
+                      color="primary"
+                      clearable
+                      @keydown.enter.prevent="addEmailToSelection"
+                    />
+                    <v-btn
+                      class="ml-2"
+                      icon
+                      variant="outlined"
+                      :disabled="!emailInput.trim()"
+                      @click="addEmailToSelection"
+                      ><v-icon>mdi-plus</v-icon></v-btn
+                    >
+                  </v-row>
+
+                  <div v-if="comboboxModel.length" class="mt-3">
+                    <div class="text-caption text-grey-darken-1 mb-2">
+                      {{ $t('UsabilityCooperators.addedParticipants') }}
+                    </div>
+                    <v-chip-group>
                       <v-chip
-                        v-bind="props"
+                        v-for="(item, i) in comboboxModel"
+                        :key="i"
                         closable
                         color="primary"
                         variant="tonal"
                         size="small"
+                        @click:close="removeEmail(i)"
                       >
-                        <v-avatar start>
-                          <span class="text-caption">
-                            {{
-                              (typeof item.raw === 'object'
-                                ? item.raw.email
-                                : item.raw
-                              )
-                                .charAt(0)
-                                .toUpperCase()
-                            }}
-                          </span>
-                        </v-avatar>
-                        {{
-                          typeof item.raw === 'object'
-                            ? item.raw.email
-                            : item.raw
-                        }}
+                        {{ item.email }}
                       </v-chip>
-                    </template>
-                    <template #item="{ props, item }">
-                      <v-list-item
-                        v-bind="props"
-                        :title="item.raw.email"
-                        :subtitle="item.raw.name || 'Registered user'"
-                        class="participant-item"
-                      >
-                        <template #prepend>
-                          <v-avatar size="40" color="primary" class="mr-3">
-                            <span class="text-white font-weight-bold">
-                              {{ item.raw.email.charAt(0).toUpperCase() }}
-                            </span>
-                          </v-avatar>
-                        </template>
-                        <template #append>
-                          <v-chip
-                            v-if="isEmailAlreadySelected(item.raw.email)"
-                            size="small"
-                            color="success"
-                            variant="tonal"
-                          >
-                            Selected
-                          </v-chip>
-                          <v-chip
-                            v-else-if="isParticipantAlreadyInvited(item.raw.id)"
-                            size="small"
-                            color="warning"
-                            variant="tonal"
-                          >
-                            Already Invited
-                          </v-chip>
-                        </template>
-                      </v-list-item>
-                    </template>
-                    <template #no-data>
-                      <div class="pa-4 text-center">
-                        <v-icon size="48" color="primary" class="mb-2">
-                          mdi-email-plus-outline
-                        </v-icon>
-                        <p class="text-body-2 text-grey-darken-1 mb-1">
-                          Type any email address and press Enter
-                        </p>
-                        <p class="text-caption text-grey">
-                          You can invite anyone, not just registered users
-                        </p>
-                      </div>
-                    </template>
-                  </v-combobox>
+                    </v-chip-group>
+                  </div>
                 </div>
 
                 <!-- Schedule Section -->
@@ -170,7 +119,7 @@
                     {{ $t('UsabilityCooperators.scheduledAt') }}
                   </div>
                   <p class="field-description mb-3">
-                    Choose the date and time for the evaluation session.
+                    {{ $t('UsabilityCooperators.scheduleDescription') }}
                   </p>
 
                   <v-row class="mt-2">
@@ -191,7 +140,13 @@
                             density="comfortable"
                             prepend-inner-icon="mdi-calendar"
                             placeholder="Select date"
-                            :rules="[(v) => !!v || 'Date is required']"
+                            :rules="[
+                              (v) =>
+                                !!v ||
+                                t(
+                                  'UsabilityCooperators.validation.dateRequired',
+                                ),
+                            ]"
                             required
                           />
                         </template>
@@ -252,7 +207,7 @@
                     {{ $t('UsabilityCooperators.inviteMessage') }}
                   </div>
                   <p class="field-description mb-3">
-                    Write a personalized message to include with the invitation.
+                    {{ $t('UsabilityCooperators.inviteMessageDescription') }}
                   </p>
                   <v-textarea
                     v-model="inviteMessage"
@@ -283,7 +238,9 @@
                   <v-icon class="mr-2" size="24" color="primary"
                     >mdi-eye-outline</v-icon
                   >
-                  <h3 class="text-h6 font-weight-bold">Invitation Preview</h3>
+                  <h3 class="text-h6 font-weight-bold">
+                    {{ $t('UsabilityCooperators.invitationPreview') }}
+                  </h3>
                 </div>
 
                 <v-card class="invitation-preview elevation-2" border>
@@ -291,13 +248,15 @@
                     <v-icon class="mr-2" color="primary"
                       >mdi-email-outline</v-icon
                     >
-                    <span class="text-subtitle-1">Evaluation Invitation</span>
+                    <span class="text-subtitle-1">
+                      {{ $t('UsabilityCooperators.evaluationInvitation') }}
+                    </span>
                   </v-card-title>
 
                   <v-card-text class="pa-4">
                     <div class="preview-content">
                       <p class="text-body-2 mb-3">
-                        <strong>To:</strong>
+                        <strong>{{ $t('UsabilityCooperators.to') }}:</strong>
                         <v-chip-group>
                           <v-chip
                             v-for="(item, i) in comboboxModel"
@@ -308,19 +267,26 @@
                           >
                             {{ typeof item === 'object' ? item.email : item }}
                           </v-chip>
-                          <span v-if="!comboboxModel.length"
-                            >No participant selected</span
-                          >
+                          <span v-if="!comboboxModel.length">{{
+                            $t('UsabilityCooperators.noParticipantSelected')
+                          }}</span>
                         </v-chip-group>
                       </p>
                       <p class="text-body-2 mb-3">
-                        <strong>Scheduled:</strong>
+                        <strong
+                          >{{ $t('UsabilityCooperators.scheduled') }}:</strong
+                        >
                         {{ formattedDateTime || 'No date/time selected' }}
                       </p>
                       <div class="mb-3">
-                        <strong class="text-body-2">Message:</strong>
+                        <strong class="text-body-2"
+                          >{{ $t('UsabilityCooperators.message') }}:</strong
+                        >
                         <div class="mt-1 pa-3 bg-grey-lighten-5 rounded">
-                          {{ inviteMessage || 'No message entered yet...' }}
+                          {{
+                            inviteMessage ||
+                            $t('UsabilityCooperators.noMessageYet')
+                          }}
                         </div>
                       </div>
                     </div>
@@ -334,12 +300,12 @@
                     class="mb-4"
                     icon="mdi-information-outline"
                   >
-                    <v-alert-title>{{
-                      $t('UsabilityCooperators.inviteInfo')
-                    }}</v-alert-title>
+                    <v-alert-title>
+                      {{ $t('UsabilityCooperators.inviteInfoTitle') }}
+                    </v-alert-title>
+
                     <div class="text-body-2 mt-2">
-                      The participant will receive an email notification and can
-                      accept or decline the invitation.
+                      {{ $t('UsabilityCooperators.inviteInfoDescription') }}
                     </div>
                   </v-alert>
                 </div>
@@ -357,7 +323,7 @@
             size="large"
             @click="$emit('update:dialog', false)"
           >
-            Cancel
+            {{ $t('common.cancel') }}
           </v-btn>
           <v-btn
             color="primary"
@@ -382,11 +348,17 @@ import EmailController from '@/shared/controllers/EmailController'
 import { computed, ref } from 'vue'
 import { useStore } from 'vuex'
 import { ACCESS_LEVEL } from '../../../../shared/utils/accessLevel'
-import { useCooperatorUtils } from '@/shared/composables/useCooperatorUtils'
+import {
+  useCooperatorUtils,
+  normalizeCooperatorInviteEntry,
+} from '@/shared/composables/useCooperatorUtils'
 import { showError, showSuccess } from '@/shared/utils/toast'
+import { useI18n } from 'vue-i18n'
+
+const { t } = useI18n()
 
 // Props
-const props = defineProps({
+defineProps({
   dialog: Boolean,
 })
 
@@ -397,7 +369,7 @@ const emit = defineEmits(['update:dialog'])
 const store = useStore()
 
 // Composables
-const { validateEmail } = useCooperatorUtils()
+const { validateEmail: validateEmailFormat } = useCooperatorUtils()
 
 // Helper functions
 const getDefaultTime = () => {
@@ -421,24 +393,29 @@ const hour = ref(getDefaultTime())
 const inviteForm = ref(null)
 const valid = ref(false)
 const comboboxModel = ref([])
+const emailInput = ref('')
 const inviteMessage = ref('')
 const loading = ref(false)
 const selectedRole = ref(ACCESS_LEVEL.ADMIN)
 
-const roleOptions = [
+const roleOptions = computed(() => [
   {
-    label: 'Evaluator',
+    label: t('UsabilityCooperators.roles.evaluator'),
     value: ACCESS_LEVEL.EVALUATOR,
-    description: 'Participates in the test, shares screen/video.',
+    description: t('UsabilityCooperators.roles.evaluatorDesc'),
   },
   {
-    label: 'Observator',
+    label: t('UsabilityCooperators.roles.observator'),
     value: ACCESS_LEVEL.OBSERVATOR,
-    description: 'Watches the session silently, takes notes.',
+    description: t('UsabilityCooperators.roles.observatorDesc'),
   },
-]
+])
 
 // Computed
+const users = computed(() =>
+  test.value?.cooperators ? [...test.value.cooperators] : [],
+)
+
 const minTime = computed(() => {
   const currentDate = new Date()
   currentDate.setDate(currentDate.getDate() - 1)
@@ -455,30 +432,12 @@ const minTime = computed(() => {
   }
 })
 
+const test = computed(() => store.getters.test)
+
 const cooperatorsEdit = computed(() =>
   test.value?.cooperators ? [...test.value.cooperators] : [],
 )
 
-const test = computed(() => store.getters.test)
-const users = computed(() => store.state.Users?.users || [])
-
-const filteredUsers = computed(() => {
-  if (!users.value || users.value.length === 0) return []
-
-  return users.value
-    .filter((user) => user && user.email) // Filter out invalid users
-    .map((user) => ({
-      ...user,
-      displayText: user.name ? `${user.email} (${user.name})` : user.email,
-    }))
-    .sort((a, b) => {
-      // Sort by email alphabetically with null checks
-      const emailA = a.email || ''
-      const emailB = b.email || ''
-      return emailA.localeCompare(emailB)
-    })
-})
-
 const formattedDateTime = computed(() => {
   if (!date.value || !hour.value) return ''
 
@@ -504,27 +463,46 @@ const formattedDateTime = computed(() => {
 })
 
 // Methods
-const isParticipantAlreadyInvited = (userId) => {
-  if (!userId || !cooperatorsEdit.value) return false
-  return cooperatorsEdit.value.some(
-    (cooperator) => cooperator && cooperator.userDocId === userId,
-  )
+const isEmailAlreadySelected = (email) =>
+  comboboxModel.value.some((item) => item === email)
+
+const removeEmail = (index) => {
+  comboboxModel.value.splice(index, 1)
 }
 
-const isEmailAlreadySelected = (email) =>
-  comboboxModel.value.some(
-    (item) => (typeof item === 'object' ? item.email : item) === email,
-  )
-
-const validateEmailInput = () => {
-  comboboxModel.value = comboboxModel.value.filter((item) => {
-    const email = typeof item === 'object' ? item.email : item
-    if (!validateEmail(email)) {
-      showError('Invalid email: ' + email)
-      return false
-    }
-    return true
-  })
+const addEmailToSelection = () => {
+  const email = emailInput.value.trim()
+  if (!email) return
+
+  if (!validateEmailFormat(email)) {
+    showError(t('UsabilityCooperators.validation.invalidEmail', { email }))
+    emailInput.value = ''
+    return
+  }
+
+  const validationError =
+    useCooperatorUtils().getCooperatorInviteValidationError({
+      email,
+      currentUserEmail: store.getters.user?.email,
+      studyOwnerEmail: test.value?.testAdmin?.email,
+      existingCooperators: cooperatorsEdit.value,
+      t,
+    })
+
+  if (validationError) {
+    showError(validationError)
+    emailInput.value = ''
+    return
+  }
+
+  if (isEmailAlreadySelected(email)) {
+    showError('This email has already been added.')
+    emailInput.value = ''
+    return
+  }
+
+  comboboxModel.value.push(normalizeCooperatorInviteEntry(email, users.value))
+  emailInput.value = ''
 }
 
 const saveInvitation = async () => {
@@ -553,13 +531,6 @@ const saveInvitation = async () => {
 
     // Construct datetime string with proper validation
     const dateTimeString = `${dateValue}T${timeValue}:00`
-    console.log('Constructing datetime from:', {
-      originalDate: date.value,
-      formattedDate: dateValue,
-      hour: hour.value,
-      dateTimeString,
-    })
-
     const dateTime = new Date(dateTimeString)
 
     // Check if the constructed date is valid
@@ -568,17 +539,20 @@ const saveInvitation = async () => {
     }
 
     const timestamp = dateTime.toISOString()
-    // Loopin through all selected emails/users
+    // Loop through all selected emails/users
     comboboxModel.value.forEach((item) => {
-      const email = typeof item === 'object' ? item.email : item
-      const userDocId = typeof item === 'object' ? item.id : null
-
-      // Prevnt duplicate invites
-      if (
-        !cooperatorsEdit.value.some(
-          (c) => c.email === email && c.testDate === timestamp,
-        )
-      ) {
+      const normalizedEntry = normalizeCooperatorInviteEntry(item, users.value)
+      const email =
+        normalizedEntry.email || (typeof item === 'object' ? item.email : item)
+      const userDocId =
+        normalizedEntry.userDocId || (typeof item === 'object' ? item.id : null)
+
+      // Prevent duplicate invites
+      const alreadyExists = cooperatorsEdit.value.some(
+        (c) => c.email === email && c.testDate === timestamp,
+      )
+
+      if (!alreadyExists) {
         cooperatorsEdit.value.push(
           new Cooperators({
             userDocId,
@@ -596,7 +570,6 @@ const saveInvitation = async () => {
     })
     await submit()
   } catch (error) {
-    console.error('Error saving invitation:', error)
     showError(error.message)
   } finally {
     loading.value = false
@@ -612,9 +585,7 @@ const submit = async () => {
     if (!guest.accepted) {
       try {
         await notifyCooperator(guest)
-      } catch (err) {
-        console.error('notfyCooperator error:', err)
-      }
+      } catch {}
     }
   }
 
@@ -626,6 +597,7 @@ const submit = async () => {
 
   inviteMessage.value = ''
   comboboxModel.value = []
+  emailInput.value = ''
   selectedRole.value = ACCESS_LEVEL.ADMIN
 
   emit('update:dialog', false)
@@ -653,8 +625,7 @@ const notifyCooperator = async (guest) => {
         }),
       })
       showSuccess('Notification sent successfully')
-    } catch (err) {
-      console.error('addNotification failed:', err)
+    } catch {
       showError('Failed to send notification')
     }
     return
@@ -681,8 +652,7 @@ const notifyCooperator = async (guest) => {
       },
     })
     showSuccess('Email invitation sent')
-  } catch (err) {
-    console.error('External email send failed:', err)
+  } catch {
     showError('Failed to send email invitation')
   }
 }
diff --git a/tests/unit/cooperatorInviteValidation.spec.js b/tests/unit/cooperatorInviteValidation.spec.js
new file mode 100644
index 000000000..e7eed7343
--- /dev/null
+++ b/tests/unit/cooperatorInviteValidation.spec.js
@@ -0,0 +1,82 @@
+import {
+  getCooperatorInviteValidationError,
+  normalizeCooperatorInviteEntry,
+} from '@/shared/composables/useCooperatorUtils'
+
+const t = (key) => {
+  const messages = {
+    'cooperators.validation.invalidEmail':
+      'Please enter a valid email address.',
+    'cooperators.validation.invalidFormat':
+      'Please enter a valid email address.',
+    'cooperators.validation.inviteSelf': 'You cannot invite yourself.',
+    'cooperators.validation.inviteOwner':
+      'The study owner cannot be invited as a cooperator.',
+    'cooperators.validation.alreadyCooperator':
+      'This email is already a cooperator for this study.',
+  }
+
+  return messages[key]
+}
+
+describe('getCooperatorInviteValidationError', () => {
+  it('rejects invalid email addresses', () => {
+    const result = getCooperatorInviteValidationError({
+      email: 'invalid-email',
+      currentUserEmail: 'owner@example.com',
+      studyOwnerEmail: 'study-owner@example.com',
+      existingCooperators: [],
+      t,
+    })
+
+    expect(result).toBe('Please enter a valid email address.')
+  })
+
+  it('rejects inviting the logged in user', () => {
+    const result = getCooperatorInviteValidationError({
+      email: 'me@example.com',
+      currentUserEmail: 'me@example.com',
+      studyOwnerEmail: 'study-owner@example.com',
+      existingCooperators: [],
+      t,
+    })
+
+    expect(result).toBe('You cannot invite yourself.')
+  })
+
+  it('rejects inviting the study owner', () => {
+    const result = getCooperatorInviteValidationError({
+      email: 'study-owner@example.com',
+      currentUserEmail: 'me@example.com',
+      studyOwnerEmail: 'study-owner@example.com',
+      existingCooperators: [],
+      t,
+    })
+
+    expect(result).toBe('The study owner cannot be invited as a cooperator.')
+  })
+
+  it('rejects inviting someone already listed as a cooperator', () => {
+    const result = getCooperatorInviteValidationError({
+      email: 'existing@example.com',
+      currentUserEmail: 'me@example.com',
+      studyOwnerEmail: 'study-owner@example.com',
+      existingCooperators: [{ email: 'existing@example.com' }],
+      t,
+    })
+
+    expect(result).toBe('This email is already a cooperator for this study.')
+  })
+
+  it('returns null for valid email', () => {
+    const result = getCooperatorInviteValidationError({
+      email: 'registered@example.com',
+      currentUserEmail: 'me@example.com',
+      studyOwnerEmail: 'study-owner@example.com',
+      existingCooperators: [],
+      t,
+    })
+
+    expect(result).toBeNull()
+  })
+})