title: PayPal Adaptive Payment Api pre-populate user data
body: <p>I am making a website where we are going to host events and would like a user "USER A" to be able to start an event - enter their paypal account info and set a price.  Then other users can register for their event and pay USER A directly, with out us having to process their credit card.  We would like users that do not have paypal accounts to be able to pay with a credit card.</p>
  
  <p>It looks like Paypal's Adaptive Payment is the best API for us to use to accomplish this.  I have it working in the sandbox environment.  My problem is this - a user clicks to register for USER A's event , then they enter all their info (name, address, company, ect.)  we need to keep this info in our Database so this needs to be done first.  Then they will click on a button that says  "Pay with Paypal".   This creates a paykey and redirects the user to the Paypal login page where the user has 2 options (a. login paypal or b. enter personal info again and credit card information)  </p>
  
  <p>I want to know how I can accomplish having all the fields already filled out in the Paypal page , so the user does not have to enter all of their information again.  They will be able to delete data in the text boxes if the billing address happens to be different.  But all websites I have ever seen to not make the user enter this information twice if they are identical.  Now I know this is possible because I have seen other sites do it.  I have looked into SetPaymentOptions API , but it is not very clear how that works , and I need user information to be passed even if they are not known to Paypal already.</p>
  
  <p>I tried adding values as suggested in Paypal tutorials like this</p>
  
  <pre><code>&lt;INPUT TYPE="hidden" NAME="first_name" VALUE="John"&gt;
  &lt;INPUT TYPE="hidden" NAME="last_name" VALUE="Doe"&gt;
  &lt;INPUT TYPE="hidden" NAME="address1" VALUE="9 Elm Street"&gt;
  </code></pre>
  
  <p>but that didn't work, Here is the raw data from Fiddler from the request :</p>
  
  <pre><code>POST https://svcs.sandbox.paypal.com/AdaptivePayments/Pay HTTP/1.1
  Content-Type: text/xml;charset=utf-8
  X-PAYPAL-SECURITY-USERID: scotts_XXXXXXXXX_biz_api1.live.com
  X-PAYPAL-SECURITY-PASSWORD: 1344XXXXX
  X-PAYPAL-SECURITY-SIGNATURE: AOLbPDojAEUdeQJ3wXagJXkxYeJDARg4IXXXXXXXXXXXXXXXXXXX
  X-PAYPAL-SERVICE-VERSION: 1.1.0
  X-PAYPAL-APPLICATION-ID: APP-80W2844XXXXXXXXX
  X-PAYPAL-REQUEST-DATA-FORMAT: XML
  X-PAYPAL-RESPONSE-DATA-FORMAT: XML
  Host: svcs.sandbox.paypal.com
  Content-Length: 810
  Expect: 100-continue
  Connection: Keep-Alive
  </code></pre>