How to know when a user to a referred site signs up with or purchases from them?
<p>I am in the process of developing a PHP application that awards users for supporting indie games. Once my website confirms an indie purchase, it will unlock certain VIP areas of my site. </p>

<p>For example, I would have a link on my website to Minecraft's registration page. Once my referred user signs up and pays for his copy of Minecraft, is there any way for my site to instantly be updated that the user successfully bought a copy?</p>

<p>This isn't specific to Minecraft either. I would need to include many links to other indie developers' purchase pages.</p>

<p>I'm at a loss to where to begin on this, nor even sure if it's technically possible. </p>
