title: PHP PayPal Subscription with IPN
body: <p>I am trying to learn how I can add PayPal Subscription to my existing PHP app using IPN and looking for a good article that explains the ins-and-outs.</p>
  
  <p>In my app, users can register for a free account and then they can select a membership type and rate (daily, weekly, monthly and yearly). When they have made their selection, the configured PayPal button is displayed. They can click the Subscribe button which takes them to PayPal.</p>
  
  <p>I need to know how to identify the user: what custom information to send to PayPal that is then sent back? I would also like to know what information PayPal sends back to the IPN page.</p>
  
  <p>It seems that the button can be configured for the notify url. Does that mean I still have to turn on IPN?</p>
  
  <p>I just have too many questions to list here... The PayPal site does not have any teaching material that explains Subscriptions and how to integrate it into a site.</p>
  
  <p><strong>Any good and recent articles you know of?</strong></p>