title: how does Auto-renewable in app purchase / subscription renew itself in iphone
body: <p>I am trying to understand how the auto-renewal part works. So far i went through</p>
  
  <p><a href="https://stackoverflow.com/questions/1298998/verify-receipt-for-in-app-purchase">Verify receipt for in App purchase</a></p>
  
  <p><a href="http://www.phpriot.com/articles/verifying-app-store-receipts-php-curl" rel="nofollow noreferrer">http://www.phpriot.com/articles/verifying-app-store-receipts-php-curl</a></p>
  
  <p>and Apple Documentation. I have got the App purchasing part complete but am not able to get the auto-renewal flow of it.</p>
  
  <p>when the purchase expires the apple server response has status:21002 the receipt is valid but has expired. </p>
  
  <p>what i am trying to understand is 
  WHO triggers the new purchase? app store itself in the backend?
  How does the app get to know that renewal has happened? or in other words, how does the renewal certificate reach application for processing?</p>
  
  <p>Br,
  Darshan</p>