Payment Configuration -> Payment Settings screen, please take special note of the setting
named "Is a Security Code Required for Credit Cards?".
This is a global setting that all of SoftSlate Commerce's payment processors that ask for credit card information, including the Basic Payment Processor and Payflow Link and Payflow Pro processors, use when validating the user's submission of credit card information.
If it's set to "yes", the user must submit a security code with the credit card number. The security code is the three- or four-digit number on the back of the credit card. It is also variously known as the CVV2, CVC2, or CID number.