American Express does not check for CVV codes by default. Merchants who use the Kosmospay system to go through the Mercury Gateway in xcart must sign up for the CVV checking service directly through AMEX or opt out of CVV checking in the back of x-cart to be able to process American Express cards.
The following is from the pdf listed below (found on the American Express web site):
"Note the Card Identification Number (CID). Your merchant account must be certified to verify the CID number. To inquire more about the program, send an e-mail to firstname.lastname@example.org."
X-cart customers who choose not to verify CVV (called CID above) codes through AMEX, and who use the Mercury gateway and the Kosmos Payment system, must choose "CVV Not Processed (AMEX Cards)" in the "Charge order if the result of CVV check-up is:" field in the back end of xcart.
To get to the page containing this field: 1) Log into the administrator section of xcart. 2) Click on the "Payment Methods" link in the "Administration" sidebar menu, or go to: