When entering back office transactions and paying with payment method of credit card, there is a field for CSC. This is 3 or 4 digit Card Security Code on the back of the credit card. This solutions explains when it is necessary to enter this code.
If the CSC level for your merchant account is set to None, a CSC code is not required for back office transactions. If your CSC settings are set to Light or Full, a CSC code is required for all back office transactions.
To check your CSC level, follow these steps:
Go to Revenue > Blackbaud Payment Service merchant accounts.
Highlight the merchant account defined here and click Edit.
In the CSC level field, see if None, Light, or Full is selected.