Why is Google sign in failing in my app?

Google sign-in can fail for a lot of different reasons, and the fix depends on the exact error you’re seeing. Here are the most common causes and what to check:

Common causes

1. OAuth client ID mismatch

   • You may be using the wrong client ID for your platform:
     • Android client ID for Android
     • iOS client ID for iOS
     • Web client ID for backend/auth exchange
   • A mismatch often causes DEVELOPER_ERROR, invalid_client, or sign-in just silently failing.

2. SHA-1 / SHA-256 not configured

   • For Android, your app’s signing certificate fingerprint must be added in the Google Cloud Console / Firebase project.
   • If you’re using debug build, you need the debug SHA-1 too.

3. Package name / bundle ID mismatch

   • The app’s package name (Android) or bundle ID (iOS) must exactly match what’s registered in Google/Firebase.

4. Google Sign-In API not enabled

   • In Google Cloud Console, the relevant APIs or Google Identity services may not be enabled.

5. Wrong configuration file

   • Android: google-services.json
   • iOS: GoogleService-Info.plist
   • If these files are outdated or from the wrong project, sign-in fails.

6. Missing OAuth consent screen / test user setup

   • If your app is in testing mode, only added test users can sign in.

7. Incorrect redirect URI / web client setup

   • Common in Flutter, React Native, web, or auth-backend flows.
   • The redirect URI must match exactly what Google expects.

8. Network / Play Services issues

   • On Android, outdated or missing Google Play Services can block sign-in.

9. Library version incompatibility

   • Old auth libraries can break with newer Google Identity requirements.

10. Firebase/Auth backend mismatch

• If you sign in with Google and then exchange the token with Firebase/Auth server, the token audience/client ID must match.

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What I need from you to pinpoint it

Please send:

• The exact error message or stack trace
• Your platform: Android / iOS / Web / Flutter / React Native / etc.
• Whether you’re using Firebase Auth or Google Sign-In directly
• Relevant config snippets:
  • Android build.gradle
  • google-services.json/GoogleService-Info.plist status
  • Sign-in code

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Quick checks for Android

• Confirm applicationId matches the Firebase/Google Console package name
• Add debug SHA-1 and release SHA-1
• Re-download google-services.json
• Make sure Google Play Services is installed/up to date
• Ensure you’re using the correct webClientId if your SDK requires it

If you paste the error and your sign-in code, I can tell you the likely root cause pretty quickly.