see: https://github.com/Backendless/Android-SDK/issues/219
This method GoogleAuthUtil.getToken(context, string, string) which is being used https://github.com/Backendless/Android-SDK/blob/master/samples/LoginWithGooglePlusSDK/app/src/main/java/com/backendless/example/loginwithgoogleplussdk/app/LoginFragment.java#L162, is depreciated.
Can you update the sample to show the new way to login? I’ve also raised http://stackoverflow.com/questions/38497317/auth-googlesigninapi-as-googleauthutil-replacement-for-google-plus-sign-in on how to get the token.
See google migration guide:
https://developers.google.com/identity/sign-in/android/migration-guide