Make sure your SHA-1 signing key is the same as the Google Play Console and Google Cloud Console or Firebase SHA-1 fingerprint.

1. Go to Google Play Console

2. Select your app

3. Navigate to:
   Release > Setup > App Integrity

4. Under App Signing, copy the SHA-1 (App signing key)

5. Go to Google Cloud Console

6. Open your project

7. Go to:
   APIs & Services → Credentials

8. Edit the OAuth 2.0 Client ID for your Android app

9. Add the new SHA-1 you got from the Play Console.

Note:

1. It can take 5–10 minutes for the change to propagate.

2. Internal testers may need to clear app data or reinstall.

3. Ensure the internal testers are added in your OAuth Consent Screen as test users (if app isn’t verified yet).