We offer two payment processors: Stripe and PayPal. Stripe accept most major bank cards. PayPal process payments for customers who have already signed up to their service, as well as guest payments made by bank card.
If the card details are entered accurately and the card is declined, this may be on the instruction of the issuing bank, particularly if it is an international transaction (Stitching Cards is in the United Kingdom). In this case, the advice of the payment processor is to tell the customer to try a different payment method, or they can contact their issuing bank for more information.