diff --git a/sandwich-retrofit/src/test/kotlin/com/skydoves/sandwich/ResponseTransformerTest.kt b/sandwich-retrofit/src/test/kotlin/com/skydoves/sandwich/ResponseTransformerTest.kt
index 6ce6d8b4..ef02d177 100644
--- a/sandwich-retrofit/src/test/kotlin/com/skydoves/sandwich/ResponseTransformerTest.kt
+++ b/sandwich-retrofit/src/test/kotlin/com/skydoves/sandwich/ResponseTransformerTest.kt
@@ -15,7 +15,6 @@
  */
 package com.skydoves.sandwich
 
-import com.skydoves.sandwich.ErrorEnvelopeMapper.map
 import com.skydoves.sandwich.retrofit.responseOf
 import com.skydoves.sandwich.retrofit.statusCode
 import kotlinx.coroutines.flow.first
@@ -925,7 +924,7 @@ internal class ResponseTransformerTest : ApiAbstract<DisneyService>() {
   fun validateOnSuccessPassTest() {
     val response = Response.success("foo")
     val apiResponse = ApiResponse.responseOf { response }
-    val validated = apiResponse.validate({ it.length > 2 }) { "Too short" }
+    val validated = apiResponse.validate({ it.length > 2 }, errorMessage = "Too short")
 
     assertThat(validated.getOrNull(), `is`("foo"))
   }
@@ -934,7 +933,7 @@ internal class ResponseTransformerTest : ApiAbstract<DisneyService>() {
   fun validateOnSuccessFailTest() {
     val response = Response.success("fo")
     val apiResponse = ApiResponse.responseOf { response }
-    val validated = apiResponse.validate({ it.length > 2 }) { "Too short" }
+    val validated = apiResponse.validate({ it.length > 2 }, errorMessage = "Too short")
 
     assertThat(validated is ApiResponse.Failure.Error, `is`(true))
   }
@@ -942,7 +941,7 @@ internal class ResponseTransformerTest : ApiAbstract<DisneyService>() {
   @Test
   fun validateOnFailureTest() {
     val apiResponse = ApiResponse.exception(Throwable("error"))
-    val validated = apiResponse.validate({ true }) { "Error" }
+    val validated = apiResponse.validate({ true }, "Error")
 
     assertThat(validated is ApiResponse.Failure.Exception, `is`(true))
   }
@@ -969,7 +968,7 @@ internal class ResponseTransformerTest : ApiAbstract<DisneyService>() {
   fun requireNotNullOnSuccessWithValueTest() {
     val response = Response.success("foo" to "bar")
     val apiResponse = ApiResponse.responseOf { response }
-    val required = apiResponse.requireNotNull({ it.first }) { "Value is null" }
+    val required = apiResponse.requireNotNull({ it.first }, "Value is null")
 
     assertThat(required.getOrNull(), `is`("foo"))
   }
@@ -978,7 +977,7 @@ internal class ResponseTransformerTest : ApiAbstract<DisneyService>() {
   fun requireNotNullOnSuccessWithNullTest() {
     val response = Response.success("foo" to null as String?)
     val apiResponse = ApiResponse.responseOf { response }
-    val required = apiResponse.requireNotNull({ it.second }) { "Value is null" }
+    val required = apiResponse.requireNotNull({ it.second }, "Value is null")
 
     assertThat(required is ApiResponse.Failure.Error, `is`(true))
   }
@@ -986,7 +985,7 @@ internal class ResponseTransformerTest : ApiAbstract<DisneyService>() {
   @Test
   fun requireNotNullOnFailureTest() {
     val apiResponse = ApiResponse.exception(Throwable("error"))
-    val required = apiResponse.requireNotNull({ it }) { "Value is null" }
+    val required = apiResponse.requireNotNull({ it }, errorMessage = "Value is null")
 
     assertThat(required is ApiResponse.Failure.Exception, `is`(true))
   }
@@ -1469,7 +1468,9 @@ internal class ResponseTransformerTest : ApiAbstract<DisneyService>() {
       onError = {},
       onException = {
         // This block should never be called
-        throw AssertionError("onException block should not be called for CancellationException")
+        throw AssertionError(
+          "onException block should not be called for CancellationException",
+        )
       },
     )
   }
diff --git a/sandwich/api/android/sandwich.api b/sandwich/api/android/sandwich.api
index 6cd8108e..50a782ba 100644
--- a/sandwich/api/android/sandwich.api
+++ b/sandwich/api/android/sandwich.api
@@ -101,8 +101,8 @@ public final class com/skydoves/sandwich/ResponseTransformer {
 	public static final synthetic fun recover (Lcom/skydoves/sandwich/ApiResponse;Ljava/lang/Object;)Lcom/skydoves/sandwich/ApiResponse;
 	public static final synthetic fun recover (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function0;)Lcom/skydoves/sandwich/ApiResponse;
 	public static final synthetic fun recoverWith (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function1;)Lcom/skydoves/sandwich/ApiResponse;
-	public static final synthetic fun requireNotNull (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function1;Lkotlin/jvm/functions/Function0;)Lcom/skydoves/sandwich/ApiResponse;
-	public static synthetic fun requireNotNull$default (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function1;Lkotlin/jvm/functions/Function0;ILjava/lang/Object;)Lcom/skydoves/sandwich/ApiResponse;
+	public static final synthetic fun requireNotNull (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function1;Ljava/lang/String;)Lcom/skydoves/sandwich/ApiResponse;
+	public static synthetic fun requireNotNull$default (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function1;Ljava/lang/String;ILjava/lang/Object;)Lcom/skydoves/sandwich/ApiResponse;
 	public static final synthetic fun suspendFilter (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function2;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
 	public static final synthetic fun suspendFilterNot (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function2;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
 	public static final synthetic fun suspendFold (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function2;Lkotlin/jvm/functions/Function2;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
@@ -138,8 +138,8 @@ public final class com/skydoves/sandwich/ResponseTransformer {
 	public static final synthetic fun toFlow (Lcom/skydoves/sandwich/ApiResponse;)Lkotlinx/coroutines/flow/Flow;
 	public static final synthetic fun toFlow (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function1;)Lkotlinx/coroutines/flow/Flow;
 	public static final synthetic fun toSuspendFlow (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function2;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
-	public static final synthetic fun validate (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function1;Lkotlin/jvm/functions/Function0;)Lcom/skydoves/sandwich/ApiResponse;
-	public static synthetic fun validate$default (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function1;Lkotlin/jvm/functions/Function0;ILjava/lang/Object;)Lcom/skydoves/sandwich/ApiResponse;
+	public static final synthetic fun validate (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function1;Ljava/lang/String;)Lcom/skydoves/sandwich/ApiResponse;
+	public static synthetic fun validate$default (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function1;Ljava/lang/String;ILjava/lang/Object;)Lcom/skydoves/sandwich/ApiResponse;
 	public static final synthetic fun zip (Lcom/skydoves/sandwich/ApiResponse;Lcom/skydoves/sandwich/ApiResponse;)Lcom/skydoves/sandwich/ApiResponse;
 	public static final synthetic fun zip (Lcom/skydoves/sandwich/ApiResponse;Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function2;)Lcom/skydoves/sandwich/ApiResponse;
 	public static final synthetic fun zip3 (Lcom/skydoves/sandwich/ApiResponse;Lcom/skydoves/sandwich/ApiResponse;Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function3;)Lcom/skydoves/sandwich/ApiResponse;
diff --git a/sandwich/api/jvm/sandwich.api b/sandwich/api/jvm/sandwich.api
index 6cd8108e..50a782ba 100644
--- a/sandwich/api/jvm/sandwich.api
+++ b/sandwich/api/jvm/sandwich.api
@@ -101,8 +101,8 @@ public final class com/skydoves/sandwich/ResponseTransformer {
 	public static final synthetic fun recover (Lcom/skydoves/sandwich/ApiResponse;Ljava/lang/Object;)Lcom/skydoves/sandwich/ApiResponse;
 	public static final synthetic fun recover (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function0;)Lcom/skydoves/sandwich/ApiResponse;
 	public static final synthetic fun recoverWith (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function1;)Lcom/skydoves/sandwich/ApiResponse;
-	public static final synthetic fun requireNotNull (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function1;Lkotlin/jvm/functions/Function0;)Lcom/skydoves/sandwich/ApiResponse;
-	public static synthetic fun requireNotNull$default (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function1;Lkotlin/jvm/functions/Function0;ILjava/lang/Object;)Lcom/skydoves/sandwich/ApiResponse;
+	public static final synthetic fun requireNotNull (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function1;Ljava/lang/String;)Lcom/skydoves/sandwich/ApiResponse;
+	public static synthetic fun requireNotNull$default (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function1;Ljava/lang/String;ILjava/lang/Object;)Lcom/skydoves/sandwich/ApiResponse;
 	public static final synthetic fun suspendFilter (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function2;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
 	public static final synthetic fun suspendFilterNot (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function2;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
 	public static final synthetic fun suspendFold (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function2;Lkotlin/jvm/functions/Function2;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
@@ -138,8 +138,8 @@ public final class com/skydoves/sandwich/ResponseTransformer {
 	public static final synthetic fun toFlow (Lcom/skydoves/sandwich/ApiResponse;)Lkotlinx/coroutines/flow/Flow;
 	public static final synthetic fun toFlow (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function1;)Lkotlinx/coroutines/flow/Flow;
 	public static final synthetic fun toSuspendFlow (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function2;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
-	public static final synthetic fun validate (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function1;Lkotlin/jvm/functions/Function0;)Lcom/skydoves/sandwich/ApiResponse;
-	public static synthetic fun validate$default (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function1;Lkotlin/jvm/functions/Function0;ILjava/lang/Object;)Lcom/skydoves/sandwich/ApiResponse;
+	public static final synthetic fun validate (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function1;Ljava/lang/String;)Lcom/skydoves/sandwich/ApiResponse;
+	public static synthetic fun validate$default (Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function1;Ljava/lang/String;ILjava/lang/Object;)Lcom/skydoves/sandwich/ApiResponse;
 	public static final synthetic fun zip (Lcom/skydoves/sandwich/ApiResponse;Lcom/skydoves/sandwich/ApiResponse;)Lcom/skydoves/sandwich/ApiResponse;
 	public static final synthetic fun zip (Lcom/skydoves/sandwich/ApiResponse;Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function2;)Lcom/skydoves/sandwich/ApiResponse;
 	public static final synthetic fun zip3 (Lcom/skydoves/sandwich/ApiResponse;Lcom/skydoves/sandwich/ApiResponse;Lcom/skydoves/sandwich/ApiResponse;Lkotlin/jvm/functions/Function3;)Lcom/skydoves/sandwich/ApiResponse;
diff --git a/sandwich/src/commonMain/kotlin/com/skydoves/sandwich/ApiResponse.kt b/sandwich/src/commonMain/kotlin/com/skydoves/sandwich/ApiResponse.kt
index d427d63e..49b6dfb1 100644
--- a/sandwich/src/commonMain/kotlin/com/skydoves/sandwich/ApiResponse.kt
+++ b/sandwich/src/commonMain/kotlin/com/skydoves/sandwich/ApiResponse.kt
@@ -22,8 +22,8 @@ import com.skydoves.sandwich.mappers.ApiResponseFailureMapper
 import com.skydoves.sandwich.mappers.ApiResponseFailureSuspendMapper
 import com.skydoves.sandwich.operators.ApiResponseOperator
 import com.skydoves.sandwich.operators.ApiResponseSuspendOperator
-import kotlin.coroutines.cancellation.CancellationException
 import kotlinx.coroutines.launch
+import kotlin.coroutines.cancellation.CancellationException
 
 /**
  * @author skydoves (Jaewoong Eum)
diff --git a/sandwich/src/commonMain/kotlin/com/skydoves/sandwich/ResponseTransformer.kt b/sandwich/src/commonMain/kotlin/com/skydoves/sandwich/ResponseTransformer.kt
index 11b90459..6875cf5f 100644
--- a/sandwich/src/commonMain/kotlin/com/skydoves/sandwich/ResponseTransformer.kt
+++ b/sandwich/src/commonMain/kotlin/com/skydoves/sandwich/ResponseTransformer.kt
@@ -24,12 +24,12 @@ import com.skydoves.sandwich.mappers.ApiResponseMapper
 import com.skydoves.sandwich.mappers.ApiSuccessModelMapper
 import com.skydoves.sandwich.operators.ApiResponseOperator
 import com.skydoves.sandwich.operators.ApiResponseSuspendOperator
-import kotlin.coroutines.cancellation.CancellationException
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.emptyFlow
 import kotlinx.coroutines.flow.flowOf
 import kotlin.contracts.InvocationKind
 import kotlin.contracts.contract
+import kotlin.coroutines.cancellation.CancellationException
 import kotlin.jvm.JvmMultifileClass
 import kotlin.jvm.JvmName
 import kotlin.jvm.JvmSynthetic
@@ -1087,21 +1087,18 @@ public suspend inline fun <T> ApiResponse<T>.suspendRecoverWith(
  * If the predicate returns false, the response is converted to [ApiResponse.Failure.Error].
  *
  * @param predicate A predicate function that validates the success data.
- * @param errorMessage A lambda that provides the error message when validation fails.
+ * @param errorMessage The error message when validation fails.
  *
  * @return The original [ApiResponse.Success] if validation passes, otherwise [ApiResponse.Failure.Error].
  */
 @JvmSynthetic
 public inline fun <T> ApiResponse<T>.validate(
   crossinline predicate: (T) -> Boolean,
-  crossinline errorMessage: () -> String = { "Validation failed" },
+  errorMessage: String = "Validation failed",
 ): ApiResponse<T> {
-  contract {
-    callsInPlace(predicate, InvocationKind.AT_MOST_ONCE)
-    callsInPlace(errorMessage, InvocationKind.AT_MOST_ONCE)
-  }
+  contract { callsInPlace(predicate, InvocationKind.AT_MOST_ONCE) }
   if (this is ApiResponse.Success && !predicate(data)) {
-    return ApiResponse.Failure.Error(payload = errorMessage())
+    return ApiResponse.Failure.Error(payload = errorMessage)
   }
   return this
 }
@@ -1137,7 +1134,7 @@ public suspend inline fun <T> ApiResponse<T>.suspendValidate(
  * If the selected value is null, the response is converted to [ApiResponse.Failure.Error].
  *
  * @param selector A selector function that extracts a nullable value from the success data.
- * @param errorMessage A lambda that provides the error message when the selected value is null.
+ * @param errorMessage The error message when the selected value is null.
  *
  * @return An [ApiResponse] with the non-null selected value, or [ApiResponse.Failure.Error] if null.
  */
@@ -1145,18 +1142,15 @@ public suspend inline fun <T> ApiResponse<T>.suspendValidate(
 @JvmSynthetic
 public inline fun <T, R> ApiResponse<T>.requireNotNull(
   crossinline selector: (T) -> R?,
-  crossinline errorMessage: () -> String = { "Required value was null" },
+  errorMessage: String = "Required value was null",
 ): ApiResponse<R> {
-  contract {
-    callsInPlace(selector, InvocationKind.AT_MOST_ONCE)
-    callsInPlace(errorMessage, InvocationKind.AT_MOST_ONCE)
-  }
+  contract { callsInPlace(selector, InvocationKind.AT_MOST_ONCE) }
   if (this is ApiResponse.Success) {
     val selected = selector(data)
     return if (selected != null) {
       ApiResponse.Success(data = selected, tag = tag)
     } else {
-      ApiResponse.Failure.Error(payload = errorMessage())
+      ApiResponse.Failure.Error(payload = errorMessage)
     }
   }
   return this as ApiResponse<R>