A “payment declined” or “card declined" message means that the issuer of the credit or debit card you have on file in your iTunes account rejected a charge or account confirmation. It is not an Apple problem; Apple is just passing through the message from your issuer. There are a number of reasons the charge or verification might be declined:
- Insufficient balance or account in arrears
- Account suspended for suspected fraud (not necessarily by you)
- Error in card number
- Wrong expiration date
- Wrong security (CVV) code
- Address in your iTunes account does not match exactly the billing address for the card
- The card was not issued in the country of the iTunes store
- You are connected through a VPN provider that does not terminate in the country of the iTunes store you are connected to.
Here is additional information from Apple→If your payment method is declined in the App Store or iTunes Store - Apple Support