Exception:
07-28 14:36:13.140: W/System.err(11382): com.google.android.gms.auth.GoogleAuthException: Unknown 07-28 14:36:13.140: W/System.err(11382): at c
I had similar problem. In my case the problem was in missed application name in google console.
Open console navigate to your project and choose "Consent screen". Fill in the "PRODUCT NAME" field and save.