368098 Paypal Automatic Add in PHP

On my RPG game, you are allowed to purchase points. When you purchase them via PayPal, right now I manually add the points but i would like to set it up so that once a user Successfully purchases the points the page they go to automatically adds their given points. They are given the option of adding 6 different amounts of points through my current paypal dropdown. -Once a user Purchase the points and are redirected to the page it I want it automatically added to the Database, so their points are added immediately. -I would like something in the code making sure that they can not just refresh the page and keep getting points (kind of like a security so they can't cheat the system) -My site is written in PHP with a MySQL DB (where the userID's are already stored and so are the Points, users must already be using our game to buy points)