title: How do I create a file to return the HTTP response 200 OK
body: <p>I'm using PayPal on my site. I've moved from Drupal to Wordpress. There is a problem with the PayPal Instant Payment Notification system from old subscribers.
  I have been told:
  "You can put an empty file which returns the HTTP response 200 OK"
  I know where the file needs to go but I have no clue how to write the contents of the file. Can anyone help?</p>