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 Q: What is CVV2 number (credit card verification number)?
VISA
Visa, Master and Discover
verification number

3-digit, non-embossed number printed on the signature panel on the back of the card immediately following the Visa card account number. This number is recorded as an additional security precaution.
VISA
American Express
Verification Number

4-digit, non-embossed number printed on the Front of the card. This number is recorded as an additional security precaution.
A wrong CVV2 number will definitely lead a declined transaction.