The payment gateway gives you Address Verification System (AVS) codes to help protect you from costly chargebacks and fraud. Whenever you perform a credit card Sale or Authorize Only transaction, the Gateway verifies the customer's address you entered on the Point of Sale page against the address that the card-issuing bank has on file for the customer. The AVS code tells you how well the two addresses match. If the transaction is approved, you will find the 3-digit alphabetic AVS code in the Approval Code (following the approval number and the reference number) on your Transaction Result page.
AVS compares the numeric portion of the street address and the zip code. If both the zip code and street address match, the 3-digit AVS code will begin with a Y. If they do not match, the AVS code will begin with an N. An N indicates a higher probability of fraud. The second character of the code will tell you more about the AVS results. You will only get an AVS code if the transaction was approved, regardless of whether the addresses match. If you get an AVS code indicating that the address and/or zip code do not match, it is up to you to decide whether you wish to accept the risk and ship the goods to the customer to complete the transaction.