Firebase Error logging in with Google. 12501 null

I solved the problem in Firebase adding the SHA1 fingerprints in the Project Settings as it is required by Google login:

To set up Google sign-in for your Android apps, you need to add the SHA1 fingerprint for each app on your Project Settings.

To get both the release and debug certificates follow the Google APIs authentication guide

I had the issue: Error logging in with Google. 10 null and found out that i mistakenly had opted to use the google play App Signing. The solution was then to copy the SHA-1 found in the google play console and enter this value into the firebase project settings.