Fix React Native Google Sign-In for Android and IOS

My React Native app’s Android build suddenly throws the familiar “DEVELOPER_ERROR – Check Android SHA-1/SHA-256 and webClientId” message after I choose an account from the Google Sign-In sheet. iOS continues to sign in fine, so the problem is isolated to Android. Still please make sure both android and ios google sign in works

Here is what I’ve already done:
• I updated both the SHA-1/SHA-256 fingerprints and the webClientId in Firebase.
• I re-downloaded the fresh google-services.json and dropped it into the android/app folder, then rebuilt an AAB and APK.
• Installation via the Play Console’s internal-testing track works up to the sign-in prompt, then fails with the error above.

Because the flow was working for months before this, I suspect a mismatch between the Play-signed keys, Firebase credentials, and the config inside react-native-google-signin, but I’m open to any other cause you uncover.

What I need from you
• Audit my Firebase project, Play Console release keys, and local keystores.
• Correct any mis-matched SHA-1/SHA-256 entries or OAuth client settings, adjust google-services.json if required, and verify the current webClientId in code.
• Patch or update the react-native-google-signin setup as needed and confirm the build.gradle tweaks are still valid for the latest React Native/Firebase versions.
• Deliver a clean build (AAB + APK) that signs in to Google successfully on an internal-test track device.

I’ll provide the current repo, Firebase access, and a test account. Once the account picker completes and auth tokens return without error on Android, I’ll consider the job done.

I'm an engineer - so one of the tasks here is to teach me how to fix this error in the future