CID

This alphanumeric field contains the three digit Visa "Card Verification Value" (CVV), MasterCard "Card Verification Code" (CVC), or four-digit American Express "Card Identification Number" (CID). This value appears as additional characters embossed on the card signature line following the credit card account number on the back of the credit card. This is an optional field which can be used to determine if the customer is actually in possession of the credit card.

Even if the CardCVV2Data is incorrect, the transaction may still be authorized. It is up to the merchant to examine the ResponseCVV2 field and decide whether to honor the transaction or not.