Some of the first characters in the credit card number are a checksum
for some of the later numbers, I believe. I am not familiar with the
algorithm enough to quote it, but there is an industry standard mod10
algorithm that can be used to determine if a card number could possibly
be a valid number (doesn't mean the card is valid, though). ShopSite may
use this test internally on the card number when it is submitted, and
display a non-JavaScript error if it doesn't pass the algorithm check.
The JavaScript function that you can see in the source of the checkout
screen, however, only checks the length of the number and the first
couple of characters.
For testing, I would suggest a Visa card number of 4111 1111 1111 1111
and any name and any (future) expiration data. This will pass any
ShopSite tests, and even most real-time credit card gateways will accept
this number when the gateway account is set to test mode.
-Loren
Larry Bohen wrote:
I had new employee place an order (like a real customer would) to
familiarize him with the order process. He entered his VISA & Discover
numbers (two separate orders) with just one of the digits (at the end)
different than his actual number. He also entered valid expiration dates....
He got "enter valid card number" messages each time. Any idea why he would
get this message?