You might have account credit that you can spend on our site from a Gift Certificate purchase, sent to you as a gift or due to a refund to your account
To use your account credit, just proceed to the first checkout page and check the box near the bottom to Use Account Credit and then continue. The next page will show the credit applied to your order and you can see the final price before completing your order.
If you have affiliate credit (different from account credit) that you are trying to redeem, please log in and see our Affiliate Program FAQ here - http://www.DriveThruRPG.com/affiliate_faq.php for more information.