This page will help you setup your licensing script with paypal. If you already have a return page set for another cart, you don't have to change it for the AF licensing script to work!
Why set up paypal? Because you must have at least one cart's return address (where the customer is returned after a successful payment and your cart records the payment using it's IPN system). If you don't already have another cart setup, then you will need to add AF licensing's return address to your paypal so paypal knows where to send the IPN notifications.
The return address is in this form (depending where you installed your AF) --- http://www.yourdomain.com/paypal/paypal.php?action=ipn
If you installed your AF licensing script in a subfolder of the same domain and named it "licensing" it would be --- http://www.yourdomain.com/licensing/paypal/paypal.php?action=ipn
Of course, you should replace the "yourdomain.com" with yours!
Now let's setup your paypal... Log into your paypal account, and click the "Profile" link in the top menu, then click on the "More Options" link from your choices. This will take you to the "Profile Summary" page.
Under the column "Selling Preferences', Click on the "Instant Payment Notification Preferences", which will take you to the "Instant Payment Notification (IPN)" page. This is where you will enable IPN and enter the url to your AF licensing script's return URL.
Choose to Turn On IPN
In the "Notification URL" field, enter the return address in the field and save it. Be sure the "Receive IPN messages (Enabled)" button is highlighted.
So, your "Notification URL" should show your AF Licensing script's return URL and the "Message delivery" should say "Enabled"!
You should now be all setup to recieve IPN notices from paypal!