 <p>EDIT: I resolved following the Google Note. LOL</p> <blockquote> <p>Note: If you are debugging your game using your debug certificate but have configured game services using your release certificate, you should add a second linked app using the same package name and your debug certificate's SHA1 fingerprint. This will allow you to sign in to the application whether it's signed with the debug or release certificates.</p> </blockquote> <p><a href="https://developers.google.com/games/services/android/troubleshooting#check_the_certificate_fingerprint">Google Services Developers Link</a></p> <p>"a second linked app" is the key point, not two game, but two linked app in the same game</p> <p>So, the right method is to link two time the same app in the Google Play Developer Console:</p> <ul> <li><p>First app with bundle com.name.appname and release fingerprint</p></li> <li><p>And a second app, with the same bundle and another name (es. AppName Test User1) and with debug fingerprint</p></li> </ul> <p>In this way, in the Api Developer Console, it creates two OAuth2 client ID for the same project and both work well.</p> <p>NOTE: If you have done many tests, remember to delete all app in the play games section of Google Play Developer Console, and all projects in the Api Developer Console.</p>