https://github.com/react-native-google-signin/google-signin/pull/737/files
https://github.com/react-native-google-signin/google-signin/issues/706#issuecomment-656126219

🔥 Issue

• google login worked in iOS but not Android

🎁 Solution

• We have to register Two SHA certificate fingerprints.
• When run cd android && ./gradlew signingReport
• It will show a few Tasks.
• Check the Store Fields on each tasks.
• Then it will show you two types of store.
  1. [project-name]/android/app/debug.keystore
  2. [home]/.android/debug.keystore
• You have to add those two task's SHA1 to firebase project's android app config