What is an AMEX or CVV2 Code?

AMEX:
All AMEX transactions require the 4 digit batch code which
is printed on the front of the card, just above the card number.

Visa and MasterCard:
Most Visa & MasterCards now have a number printed on the
back of the card, we need the last three numbers entered after
your main card number.
If your Visa or MasterCard does not have a CVV2 number on
back please enter zero "0"
In this case it may take a little longer to verify your card.