The details are here:
https://www.2checkout.com/cgi-bin/buyers/cvv.2cIn short if your card is Visa, Mastercard, or Discover card, it is a 3 digit number that appears to the right of your card number.
If you are using an American Express card, the verification number is a 4 digit number that appears on the front of your card, above and either on the left or right of the card number.
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