diff --git a/src/repository/user/userRepository.ts b/src/repository/user/userRepository.ts
index 43d245a..3ed1d55 100644
--- a/src/repository/user/userRepository.ts
+++ b/src/repository/user/userRepository.ts
@@ -86,20 +86,12 @@ export class UserRepository {
   }
 
   async findExists(studentId: string, citizenId: string): Promise<boolean> {
-    const userFromStudentId = await prisma.user.findFirst({
-      where: {
-        studentId: studentId,
-      },
-    });
-    if (userFromStudentId) {
-      return true;
-    }
-    const userFromCitizenId = await prisma.user.findFirst({
+    const user = await prisma.user.findFirst({
       where: {
-        citizenId: citizenId,
+        AND: [{ studentId: studentId }, { citizenId: citizenId }],
       },
     });
-    if (userFromCitizenId) {
+    if (user) {
       return true;
     }
     return false;
diff --git a/src/router/groupRouter.ts b/src/router/groupRouter.ts
index 3479bb5..8512dbf 100644
--- a/src/router/groupRouter.ts
+++ b/src/router/groupRouter.ts
@@ -62,7 +62,7 @@ export class GroupRouter extends BaseRouter {
       this.groupController.setHousePreferences.bind(this.groupController)
     );
 
-    this.router.get(
+    this.router.post(
       "/groupByInviteCode",
       this.groupController.getGroupByInviteCode.bind(this.groupController)
     );
diff --git a/src/usecase/auth/authUsecase.ts b/src/usecase/auth/authUsecase.ts
index 79dcea7..9d7895d 100644
--- a/src/usecase/auth/authUsecase.ts
+++ b/src/usecase/auth/authUsecase.ts
@@ -29,7 +29,7 @@ export class AuthUsecase {
     );
     if (existingUser) {
       throw new AppError(
-        "User with this student ID or citizen ID already exists",
+        "User with this student ID and citizen ID already exists",
         400
       );
     }