With our old X-Cart, we were using OnePageCheckout, which did a verification (Luhn's calc) of the entered credit card number before attempting to run it.
Then, it displayed a message that the number itself was invalid, to distinguish it from a decline.
With our new 4.7.7 with X-Payments, we just get a generic message.
Is there a way to enable a Luhn calc type check here?
More info about the algorithm is here: