diff --git a/packages/core/src/routes/custom-phrase.test.ts b/packages/core/src/routes/custom-phrase.test.ts
index fd8347849..6e6f30e11 100644
--- a/packages/core/src/routes/custom-phrase.test.ts
+++ b/packages/core/src/routes/custom-phrase.test.ts
@@ -140,7 +140,7 @@ describe('customPhraseRoutes', () => {
       const response = await customPhraseRequest
         .put(`/custom-phrases/${mockLanguageTag}`)
         .send(translation);
-      expect(response.status).toEqual(400);
+      expect(response.status).toEqual(422);
     });
 
     it('should call upsertCustomPhrase with specified language tag', async () => {
@@ -183,9 +183,9 @@ describe('customPhraseRoutes', () => {
       expect(response.status).toEqual(404);
     });
 
-    it('should return 400 status code when specified custom phrase is used as fallback language in sign-in experience', async () => {
+    it('should return 409 status code when specified custom phrase is used as fallback language in sign-in experience', async () => {
       const response = await customPhraseRequest.delete(`/custom-phrases/${mockFallbackLanguage}`);
-      expect(response.status).toEqual(400);
+      expect(response.status).toEqual(409);
     });
 
     it('should return 400 status code when the language tag is invalid', async () => {
diff --git a/packages/core/src/routes/custom-phrase.ts b/packages/core/src/routes/custom-phrase.ts
index d1c4dcc72..cf79afdff 100644
--- a/packages/core/src/routes/custom-phrase.ts
+++ b/packages/core/src/routes/custom-phrase.ts
@@ -48,7 +48,7 @@ export default function customPhraseRoutes<T extends AuthedRouter>(
     koaGuard({
       params: object({ languageTag: languageTagGuard }),
       response: CustomPhrases.guard,
-      status: [200],
+      status: [200, 404],
     }),
     async (ctx, next) => {
       const {
@@ -67,7 +67,7 @@ export default function customPhraseRoutes<T extends AuthedRouter>(
       params: object({ languageTag: languageTagGuard }),
       body: translationGuard,
       response: CustomPhrases.guard,
-      status: [200],
+      status: [200, 422],
     }),
     async (ctx, next) => {
       const {
@@ -79,7 +79,7 @@ export default function customPhraseRoutes<T extends AuthedRouter>(
 
       assertThat(
         isStrictlyPartial(resource.en.translation, translation),
-        new RequestError('localization.invalid_translation_structure')
+        new RequestError({ code: 'localization.invalid_translation_structure', status: 422 })
       );
 
       ctx.body = await upsertCustomPhrase(languageTag, translation);
@@ -92,7 +92,7 @@ export default function customPhraseRoutes<T extends AuthedRouter>(
     '/custom-phrases/:languageTag',
     koaGuard({
       params: object({ languageTag: languageTagGuard }),
-      status: [204],
+      status: [204, 404, 409],
     }),
     async (ctx, next) => {
       const {
@@ -106,6 +106,7 @@ export default function customPhraseRoutes<T extends AuthedRouter>(
       if (fallbackLanguage === languageTag) {
         throw new RequestError({
           code: 'localization.cannot_delete_default_language',
+          status: 409,
           languageTag,
         });
       }
diff --git a/packages/core/src/routes/logto-config.ts b/packages/core/src/routes/logto-config.ts
index 7f6bbc3b0..8fc13547d 100644
--- a/packages/core/src/routes/logto-config.ts
+++ b/packages/core/src/routes/logto-config.ts
@@ -11,7 +11,7 @@ export default function logtoConfigRoutes<T extends AuthedRouter>(
 
   router.get(
     '/configs/admin-console',
-    koaGuard({ response: adminConsoleDataGuard, status: 200 }),
+    koaGuard({ response: adminConsoleDataGuard, status: [200, 404] }),
     async (ctx, next) => {
       const { value } = await getAdminConsoleConfig();
       ctx.body = value;
@@ -25,7 +25,7 @@ export default function logtoConfigRoutes<T extends AuthedRouter>(
     koaGuard({
       body: adminConsoleDataGuard.partial(),
       response: adminConsoleDataGuard,
-      status: 200,
+      status: [200, 404],
     }),
     async (ctx, next) => {
       const { value } = await updateAdminConsoleConfig(ctx.guard.body);
diff --git a/packages/core/src/routes/sign-in-experience/index.ts b/packages/core/src/routes/sign-in-experience/index.ts
index a7cdbfb21..068c61acb 100644
--- a/packages/core/src/routes/sign-in-experience/index.ts
+++ b/packages/core/src/routes/sign-in-experience/index.ts
@@ -25,7 +25,7 @@ export default function signInExperiencesRoutes<T extends AuthedRouter>(
     '/sign-in-exp',
     koaGuard({
       response: SignInExperiences.guard,
-      status: [200],
+      status: [200, 404],
     }),
     async (ctx, next) => {
       ctx.body = await findDefaultSignInExperience();
@@ -48,7 +48,7 @@ export default function signInExperiencesRoutes<T extends AuthedRouter>(
         )
         .partial(),
       response: SignInExperiences.guard,
-      status: [200],
+      status: [200, 400, 404, 422],
     }),
     async (ctx, next) => {
       const {
diff --git a/packages/integration-tests/src/tests/api/custom-phrase.test.ts b/packages/integration-tests/src/tests/api/custom-phrase.test.ts
index 133605f7b..be8b9c244 100644
--- a/packages/integration-tests/src/tests/api/custom-phrase.test.ts
+++ b/packages/integration-tests/src/tests/api/custom-phrase.test.ts
@@ -60,6 +60,12 @@ describe('custom-phrase flow', () => {
     expect(zhTranslationNew).toEqual(mockZhTranslationUpdated);
   });
 
+  it('fail to update an existing custom phrase with invalid translation keys', async () => {
+    await expect(
+      createOrUpdateCustomPhrase('zh', { ...mockZhTranslationUpdated, invalidKey: 'invalid value' })
+    ).rejects.toThrow(HTTPError);
+  });
+
   it('failed to get a custom phrase with invalid language tag (zh-ZH)', async () => {
     await expect(getCustomPhrase('zh-ZH')).rejects.toThrow(HTTPError);
   });
@@ -86,6 +92,10 @@ describe('custom-phrase flow', () => {
     await expect(deleteCustomPhrase('zh-TW')).rejects.toThrow(HTTPError);
   });
 
+  it('fail to delete a custom phrase which has been set as fallback language', async () => {
+    await expect(deleteCustomPhrase('en')).rejects.toThrow(HTTPError);
+  });
+
   it('delete all custom phrases', async () => {
     await deleteCustomPhrase('zh');
     await deleteCustomPhrase('en-US');
diff --git a/packages/integration-tests/src/tests/api/sign-in-experience.test.ts b/packages/integration-tests/src/tests/api/sign-in-experience.test.ts
index 7a55f4bf8..06021e38f 100644
--- a/packages/integration-tests/src/tests/api/sign-in-experience.test.ts
+++ b/packages/integration-tests/src/tests/api/sign-in-experience.test.ts
@@ -1,4 +1,7 @@
+import { SignInIdentifier } from '@logto/schemas';
+
 import { getSignInExperience, updateSignInExperience } from '#src/api/index.js';
+import { createResponseWithCode } from '#src/helpers/admin-tenant.js';
 
 describe('admin console sign-in experience', () => {
   it('should get sign-in experience successfully', async () => {
@@ -25,4 +28,18 @@ describe('admin console sign-in experience', () => {
     const updatedSignInExperience = await updateSignInExperience(newSignInExperience);
     expect(updatedSignInExperience).toMatchObject(newSignInExperience);
   });
+
+  it('throw 400 when fail to validate SIE', async () => {
+    const newSignInExperience = {
+      signUp: {
+        identifiers: [SignInIdentifier.Username],
+        password: false,
+        verify: false,
+      },
+    };
+
+    await expect(updateSignInExperience(newSignInExperience)).rejects.toMatchObject(
+      createResponseWithCode(400)
+    );
+  });
 });