A customer’s bank normally has special fraud prevention systems which can decline a charge if the provided card information is incorrect or invalid. The issuing bank examines such data as your customer’s account balance, spending habits, card expiration date, card verification value, etc. If the card information seems correct, recommend your customer contacting his/her bank for more details of the case. In that case, you might notice a "do not honour" payment error code in your transaction list.
Here you can find additional resources that may help you in the process and tell you more about payment processing.
If you haven't found answers to your questions here or need any further assistance, don't hesitate to contact us.