Sorry for the disappointment and poor response that was not helpful. Are you receiving a decline at the merchant terminal?
When a payment is initiated either online or at a transaction terminal, your iPhone creates an encrypted payment token. The token contains a one time use code. The token is transferred from your device to the merchant’s POS system. The token the is sent to the merchant’s credit card processor and then the Payment Network Operator (Mastercard, Visa, American Express etc.) and finally to the issuing bank. Only the issuing bank can decline a transaction/payment.
Apple does not participate in the entire process. Apple does not have the key to decrypt the token. None of the details about the transaction are ever disclosed to Apple. This is not an Apple issue.