Not able to find players with GKMatchmakerViewController

I am trying to integrate Game Center for matching players. I am using that very simple function:

 
- (void)findOpponent {
    GKMatchRequest* request = [[GKMatchRequest alloc] init];
    request.minPlayers = 2;
    request.maxPlayers = 2;
    GKMatchmakerViewController *mmvc = [[GKMatchmakerViewController alloc]
                                         initWithMatchRequest:request];
    mmvc.matchmakerDelegate = self;

    [[self viewController] presentViewController:mmvc animated:YES completion:nil];
}

I do have some callback, never called tho':

- (void)matchmakerViewController:(GKMatchmakerViewController *)viewController didFindMatch:(GKMatch *)theMatch {
    NSLog(@"he");
    [[self viewController] dismissViewControllerAnimated:NO completion:nil];
    GKMatch* match = theMatch;
    [match setDelegate:self];
    NSLog(@"Ready to start match!");
}

- (void)matchmakerViewController:(GKMatchmakerViewController *)viewController didFindPlayers:(NSArray *)playerIDs {
    NSLog(@"Super he");
}

- (void)matchmakerViewController:(GKMatchmakerViewController *)viewController didReceiveAcceptFromHostedPlayer:(NSString *)playerID {
    NSLog(@"Wow");
}

When I test onmy device (wether iPhone or iPad), both using iOS 7.1, I can open Game Center from my Application, but as soon as I click on "Play Now" I instantaneously get the error: "Failed to find players". Yet none of my callback seems to get triggered in my code. Any idea of what I am doing wrong? I did try to reset my iPad settings, logging off from iCloud, rebooting my device, etc.

Fixed.

More than creating a Provisioning Profile and enabling Game Center inside, you also need to Add your app on iTunes Connect. You need to go to an extremely strange process where it ask for the release date of your app, the price, some screen shots and icons, but once done you will be able to enable Game Center for real.