Mastercard is releasing new card numbers that start with a '2'. We know this breaks our Atlas portals.
From what I've read it the new numbers should pass the luhn algorithm.
I think there is logic in our system somewhere that checks what 'types' of cards are allowed (as configured in the payment gateway record, at least with authorize.net, visa, mastercard, amex, etc.) My guess is that this logic is checking and throwing an error on the '2' as an unsupported card type.