title: in app purchase receipt validation issue
body: <p>I have an application which supports subscription as well as pay as go features. I have facing issues with receipt validation at server side.
  If </p>
  
  <ol>
  <li>user has not subscribed and tried to download content using pay as
  you go i am getting 21002 error(passing shared secret for
  validation) </li>
  <li>If user subscribed and it was expired. now user tried to
  download pay as you go then response was 21004(not passing shared secret key)</li>
  </ol>
  
  <p>I am unable to understand when I should pass shared secret to apple server. Since we have only one apple receipt which contains consumable and subscription receipt information.</p>
  
  <p>Any help?</p>