title: PayPal Website Payments Standard API
body: <p>I assume the answer to this is in the PayPal documentation somewhere, but I've been reading it for two days and my eyes are beginning to whirl.</p>
  
  <p>For Website Payments Standard, I create a page on my site (let's call this <strong>page A</strong>) which contains a dynamically generated form which contains a bunch of hidden fields detailing the content of the cart, prices of each item included, etc. It also has a token to identify the seller id. And one visible form element: the submit image.</p>
  
  <p>The customer clicks the image, which submits the form to PayPal. PayPal do their thing (which includes posting some data back to us at a URL we define (let's call this <strong>page B</strong>)), and then returns the customer back to us (again at a URL we define (let's call this <strong>page C</strong>)).</p>
  
  <p>What I'm looking for is some sort of transaction ID. We have hits from the user on pages <strong>A</strong> and <strong>C</strong>, and a hit from PayPal on page <strong>B</strong>. How do we know these three hits apply to the same transaction? (The hit on page <strong>C</strong> may not happen, of course.)</p>
  
  <hr>
  
  <p>In a separate question, am I the only one who thinks PayPal documentation is confusingly written?</p>