SubmitScoreToGameCenter.kt

GKScore gkScore = GKScore.alloc();
gkScore = gkScore.initWithLeaderboardIdentifier("my.identifier");
gkScore.setValue(42);
NSArray<GKScore> nsArray = (NSArray<GKScore>) NSArray.arrayWithObject(gkScore);
GKScore.reportScoresWithCompletionHandler(nsArray, new GKScore.Block_reportScoresWithCompletionHandler() {
    @Override
    public void call_reportScoresWithCompletionHandler(NSError nsError) {
        if (nsError != null) {
            //submitted score not successfully
        } else {
            //submitted score successfully
        }
    }
});