The Decline CVV2/CID Fail response means that the CVV code entered when checking out is invalid. The CVV code is the 3 digit code on the back of a MasterCard or Visa. In the case of an American Express, it will be the 4 digit code on the front of the card. Sometimes these number can become worn, so you can double check the code and try again. If it fails again, you will need to contact the credit card provider to verify the CVV code or try another payment method.