Generally when it comes to refunding to an expired credit card, there can be two outcomes that can occur. If the credit card is expired AND closed, then the financial institution will decline the refund. If the card is somehow renewed and was recently closed, financial institutions will provide a way for the customer to get that refund back in an alternative way. Your result may vary between credit company and financial institution that you are dealing with.It also may vary based on what payment gateway the transaction went through and whether or not they have some functionality within their business that handles tricky situations such as this one. The best step is to check with your payment gateway directly as they will have a closer understanding on how to proceed further with this case. If the payment gateway says that they are able to handle that type of refund to an expired credit card, then you should be able to safely refund through Checkfront, if not, then I would not recommend using refund in Checkfront and to contact the payment gateway and find out how to proceed.