gapi.load('auth2', function() {
    GA = gapi.auth2.init({
            client_id: "...",
            scope: "https://www.googleapis.com/auth/plus.login https://www.googleapis.com/auth/plus.me https://www.googleapis.com/auth/games"});
});

GA.signIn()

gapi.client.games.scores.submit

{
 "error": {
  "errors": [
   {
    "domain": "global",
    "reason": "UserRegistrationIncomplete",
    "message": "User has not completed registration."
   }
  ],
  "code": 401,
  "message": "User has not completed registration."
 }
}