I'm making a few improvements to an e-commerce site and it seems customers will occasionally not enter the issue number of their card (it is not a required field as Visa, MC, Amex etc does not have them), causing payment to be rejected. It seems UK Maestro and Switch cards can have issue numbers, but I found a couple of references saying that they do not all have them. Does anyone know a way to work out whether a card definitely needs an issue number before actually trying to process a transaction?
I never saw a credit card (mostly German cards but other too) with issue number but I know they exist.