Upon cancelling a reservation there "was an error processing payment". Why was the credit card accepted to begin with if it isn't valid or expires before the event?

Upon allowing for a reservation to complete, Resiada conducts a validity check on the credit card used to guarantee the reservation to ensure that the expiration date is valid through the reservation's checkout date. If a card is declining a charge, it may be due to a card limit reached or the card being canceled by the guest, which often happens in situations involving lost cards or fraudulent activity.

In such situations, you would need to contact the guest to update the credit card information on the reservation in order to process the cancellation charge. To update a credit card on a reservation, please see Change a Credit Card on a Reservation article.