The Visa payment requires you to insert the data of a valid credit card. If the information is not valid, an error message will appear, preventing you from concluding the payment.
3.1. What's CCV/CID/CVC
Card Verification Value or Code Verification Value (CVV or CVC) or Card Identification Code (CID) is a safety guarantee for credit/debit card operations, giving a better protection against credit card fraudes.
The number is generated when the card is issued, encrypting the card number and expiry date, transforming them in a key known only to the issuer bank.
Giving this code goes to assure that the client has the card in his hands.