PHP-KeyCodes is a new product which is used to sell software license key codes, pin numbers or any pre-generated codes using PayPal. The key codes are entered into the item details and when a customer makes a purchase, the first key code is removed and sent by email to the customer. This leaves the next key code ready for the next purchase. When the number of codes reach a lower limit, an email is sent to the site administrator.
The code for the ‘buy now’ buttons can be displayed in the admin interface and then copied on to your web pages.
For details refer to: