1. Open https://console.firebase.google.com

2. Select your Firebase project

3. Select Authentication -> Sign-In method

4. Enable Google Login

5. Select Project Setting

6. Genrate SHA1 and SHA256 key

*********** For Debug App **********

Open Android Studio goto terminal and copy paste the below command lines and hit enter

keytool -list -v -keystore C:\Users\{your computer user name}\.android\debug.keystore -alias androiddebugkey -storepass android -keypass android

Then Copy Your SHA1 and SHA256 Key and paste into FIrebase

*********** For Live App **********

1. Open Google Play Console

2. Click your application.

3. Click Release Management / App Signing

4. Copy Both Key and Paste in Firebase App Setting