I'm hoping someone can point me in the right direction because I've spent days going around in circles on this.

I've built a simple Android app in Android Studio. I want users to be able to sign in with their Google account so I can store favourites and settings in Firebase.

The strange thing is that everything works perfectly when I install the app directly from Android Studio:

• Credential Manager shows the Google account picker.

• User selects an account.

• Login succeeds.

• Firebase Authentication creates/updates the user.

• User data such as favourites is stored correctly.

However, if I upload exactly the same app to Google Play (I've tested Internal Testing, Closed Testing, and now Production), the login fails.

What happens:

1. User taps Sign In.

2. Google account picker appears.

3. User selects an account.

4. Login immediately fails.

In Logcat I see:

Fallback failed (GetCredentialCancellationException): [16] Account reauth failed.

Most of the advice online points to incorrect SHA fingerprints or OAuth configuration.

Currently I have added all available fingerprints to Firebase and Google Cloud Console, including:

• Upload key SHA-1

• Internal app sharing SHA-1

• App signing SHA-1

• App signing post-quantum SHA-1

• Android Studio/debug SHA-1

• Internal app sharing SHA-256

• App signing SHA-256

• App signing post-quantum SHA-256

• Android Studio/debug SHA-256

The play store version of the app I using the post-quantum SHA-1

I have also downloaded and included the latest google-services.json file in the project.

My confusion is:

• If Firebase login works when installed from Android Studio, does that confirm my Firebase Authentication setup is correct?

• What additional configuration is required for Google Play signed builds?

• Is there a common Credential Manager or Google Sign-In issue that would cause authentication to work in debug builds but fail only when installed from the Play Store?

• Is there a way to verify which SHA fingerprint Firebase is actually expecting when the Play Store version attempts to authenticate?

At this point I'm not sure whether I'm chasing a Firebase issue, a Google Cloud OAuth issue, or a Google Play App Signing issue.

Any help would be greatly appreciated.