Unfortunately we can only answer questions here, we do not have access to your account at Apple, or any of the back-end processes there. I can do my best to offer assistance, however. As for slots on Apple devices, you will need to have your Apple account up-to-date, and your credit card in good standing, and associated with your account. (If you have not entered your credit card into your iTunes account, you will need to do this first, this will allow in-app purchasing to function and make it possible to buy chips in whichever casino app you are using. See following link for directions to do this on both your portable device (phone or tablet) and computer (mac or pc).
Pay no attention to the header "Chinese Bank card" it is all the same instructions. :P