You can refund the registration by copying the refund URL, paste it in to a text editor and make the following change to the URL parameter:

Replace "refund_tr_reg" with "refund_don_reg" to load the page properly and process the refund. xxxxxx is the transaction ID of the registration you want to refund.

If you need further help with the refund or diagnosing root cause, Contact Support and provide this article number.