If you plan to incorporate Game Center into your app, it's important to correctly enable Game Center in iTunes Connect before you submit it for review.
To enable your app for Game Center, follow these steps:
Go to the Manage Game Center page from within the Manage Your Applications module in iTunes Connect and click on the Enable button. This will allow you to test your app in the sandbox and set up metadata for leaderboards and achievements.
Go to the Version Details page and click on the Enable for this Version button. This will allow this specific version of your app to access Game Center once its live on the App Store, and lets you enable or disable leaderboard, achievement and multiplayer settings on a per-version basis.