The best option is to contact the user and ask them to either update their payment details, contact their bank or arrange a direct transfer or cash payment.
If the payment failed, you can mark the credit card as invalid.
Go to Reservations > select the reservation and click on Edit > go to Payment > Report credit card as invalid:
Once you mark the card as invalid, the guest will be requested to add new card details within 24 hours.
You’ll get an email when the guest updates their details. If you don’t receive these within 24 hours, or the guest provides invalid credit card details again, you can cancel the booking with no commission.