title: Paypal + PHP: how to receive a value on success sale
body: <p>I have a paypal button on my site in a form. The form has an additional input called ID, where the user must enter a specific value.</p>
  
  <p>After the sale is complete, Paypal returns the user to domain.com/credits?done</p>
  
  <p>How can i receive the original ID value entered by the user in /credits?done ? need it to modify his database record automatically.</p>
  
  <p>Thanks.</p>