Sign-in with google for android not working in release apk

Finally solved it. I added the SHA1 key for my release key (the .jks file) in the Google Developers Console under the project registered. In Android Studio, at the left side, there is an option for Build variants under the project view. There, I changed each module to release mode (it is in debug mode by default). Then created the Signed APK by usual method, and run the app. The Google Signin worked perfectly.

When you upload an apk to the play store then play store creates a new SHA1 key called "App signing certificate". You get that SHA1 and save in your console or firebase account (as you need).

New SHA1 will be found at Released Management->App Sigining on your play console.

or

when you build signed apk with your filename.jks it has different SHA than your debug apk, put these SHA which is generated by signed apk in Firebase nd update it and again download json from firebase and override existing json from your android studio.

Before publishing app you should read Google Play launch checklist

For complete release process you can go here