This error indicates that the card has been reported as lost or stolen by the cardholder. Ideally, the card company would have you keep the card and report it back to them, but since online merchants don’t have access to cards themselves, the best course of action would be to treat the transaction like any other hard decline. Being strong indicators of fraudulent activity, it might be a good idea to reach out to your customer in the event of these errors being returned. If you can establish that the transaction and customer are legitimate, encourage your customer to reach out to his bank. On the other hand, if you can establish fraud, block the customer as soon as possible.