diff --git a/packages/core/src/routes/interaction/verifications/mandatory-user-profile-validation.test.ts b/packages/core/src/routes/interaction/verifications/mandatory-user-profile-validation.test.ts
index 3008fc565..13797b9ea 100644
--- a/packages/core/src/routes/interaction/verifications/mandatory-user-profile-validation.test.ts
+++ b/packages/core/src/routes/interaction/verifications/mandatory-user-profile-validation.test.ts
@@ -125,7 +125,7 @@ describe('validateMandatoryUserProfile', () => {
       ).resolves.not.toThrow();
     });
 
-    it('identifier includes social with verified email but email occupied should throw', async () => {
+    it('sign-in identifier includes social with verified email but email occupied should throw', async () => {
       hasUserWithEmail.mockResolvedValueOnce(true);
 
       await expect(
@@ -144,6 +144,26 @@ describe('validateMandatoryUserProfile', () => {
       );
     });
 
+    it('register identifier includes social with verified email but email occupied should throw', async () => {
+      hasUserWithEmail.mockResolvedValueOnce(true);
+
+      await expect(
+        validateMandatoryUserProfile(users, emailRequiredCtx, {
+          ...interaction,
+          event: InteractionEvent.Register,
+          identifiers: [
+            ...interaction.identifiers,
+            { key: 'social', userInfo: { email: 'email', id: 'foo' }, connectorId: 'logto' },
+          ],
+        })
+      ).rejects.toMatchError(
+        new RequestError(
+          { code: 'user.missing_profile', status: 422 },
+          { missingProfile: [MissingProfile.email] }
+        )
+      );
+    });
+
     it('identifier includes social with verified email should not throw', async () => {
       hasUserWithEmail.mockResolvedValueOnce(false);
 
@@ -200,7 +220,7 @@ describe('validateMandatoryUserProfile', () => {
       ).resolves.not.toThrow();
     });
 
-    it('identifier includes social with verified phone but phone occupied should throw', async () => {
+    it('sign-in identifier includes social with verified phone but phone occupied should throw', async () => {
       hasUserWithPhone.mockResolvedValueOnce(true);
 
       await expect(
@@ -219,6 +239,26 @@ describe('validateMandatoryUserProfile', () => {
       );
     });
 
+    it('register identifier includes social with verified phone but phone occupied should throw', async () => {
+      hasUserWithPhone.mockResolvedValueOnce(true);
+
+      await expect(
+        validateMandatoryUserProfile(users, phoneRequiredCtx, {
+          ...interaction,
+          event: InteractionEvent.Register,
+          identifiers: [
+            ...interaction.identifiers,
+            { key: 'social', userInfo: { phone: '123456', id: 'foo' }, connectorId: 'logto' },
+          ],
+        })
+      ).rejects.toMatchError(
+        new RequestError(
+          { code: 'user.missing_profile', status: 422 },
+          { missingProfile: [MissingProfile.phone] }
+        )
+      );
+    });
+
     it('identifier includes social with verified phone should not throw', async () => {
       hasUserWithPhone.mockResolvedValueOnce(false);
 
diff --git a/packages/core/src/routes/interaction/verifications/mandatory-user-profile-validation.ts b/packages/core/src/routes/interaction/verifications/mandatory-user-profile-validation.ts
index 354851093..ed24c439f 100644
--- a/packages/core/src/routes/interaction/verifications/mandatory-user-profile-validation.ts
+++ b/packages/core/src/routes/interaction/verifications/mandatory-user-profile-validation.ts
@@ -1,6 +1,7 @@
 import type { Profile, SignInExperience, User } from '@logto/schemas';
 import { InteractionEvent, MissingProfile, SignInIdentifier } from '@logto/schemas';
 import type { Nullable } from '@silverhand/essentials';
+import { conditional } from '@silverhand/essentials';
 import type { Context } from 'koa';
 
 import RequestError from '#src/errors/RequestError/index.js';
@@ -119,7 +120,7 @@ const fillMissingProfileWithSocialIdentity = async (
   interaction: MandatoryProfileValidationInteraction,
   userQueries: Queries['users']
 ): Promise<MandatoryProfileValidationInteraction> => {
-  const { identifiers, profile } = interaction;
+  const { identifiers, profile, event } = interaction;
 
   const socialUserInfo = getSocialUserInfo(identifiers);
 
@@ -144,7 +145,10 @@ const fillMissingProfileWithSocialIdentity = async (
         { code: 'user.missing_profile', status: 422 },
         {
           missingProfile: Array.from(missingProfileSet),
-          registeredSocialIdentity: { email },
+          // Throw taken email when it's sign-in event
+          ...conditional(
+            event === InteractionEvent.SignIn && { registeredSocialIdentity: { email } }
+          ),
         }
       )
     );
@@ -178,7 +182,10 @@ const fillMissingProfileWithSocialIdentity = async (
         { code: 'user.missing_profile', status: 422 },
         {
           missingProfile: Array.from(missingProfileSet),
-          registeredSocialIdentity: { phone },
+          // Throw taken phone when it's sign-in event
+          ...conditional(
+            event === InteractionEvent.SignIn && { registeredSocialIdentity: { phone } }
+          ),
         }
       )
     );
diff --git a/packages/ui/src/hooks/use-required-profile-error-handler.ts b/packages/ui/src/hooks/use-required-profile-error-handler.ts
index f7617720d..38f5e4a8f 100644
--- a/packages/ui/src/hooks/use-required-profile-error-handler.ts
+++ b/packages/ui/src/hooks/use-required-profile-error-handler.ts
@@ -27,7 +27,7 @@ const useRequiredProfileErrorHandler = ({ replace, linkSocial }: Options = {}) =
         // Required as a sign up method but missing in the user profile
         const missingProfile = data?.missingProfile[0];
 
-        // Required as a sign up method can be found in Social Identity (email / phone), but registered with a different account
+        // Required as a sign up method, verified email or phone can be found in Social Identity, but registered with a different account
         const registeredSocialIdentity = data?.registeredSocialIdentity;
 
         const linkSocialQueryString = linkSocial