A “payment 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.
You need to have a valid payment method in your account, even for free downloads. If you have no apps with in-app purchases and no subscriptions you may not need any payment method, but if you do have one it must be valid.