Re: do not enter the hypen!
"The reason for that is that credit card fields have EXACTLY 16 spaces in them.
Sometimes, you just can't fix stupid."
Nor, apparently, can you fix ignorance.
American Express card numbers have 15 digits (4 + 6 + 5), and --- several years after they introduced the 3-digit security CSC (like all the other credit/debit cards) --- I can't find a single payment service (Sage, Worldpay, any of the banks) that will allow you to specify it (the 3-digit CSC) rather than the 4-digit number that is printed on the face of the Amex Card.
In 1986 I wrote a credit card acceptance function for MUD II that stripped out the spaces and --- in every card acceptance page I have authored since then --- that continues to be the case; it seems I'm in a minority of one.