Hello @double, this is a tough one. 

In this case you would have to reach out directly to your customer to process this transaction again. If they've made a previous purchase with you and provided an email address for a receipt, our Customer Success Team can reach out to them upon your behalf. 

Unfortunately we will not be able to pull any information from the declined transaction, since the card was not processed. 

If you still have questions please feel free to reach out to me!