In order to facilitate testing, you can call this URL from your
browser or from a command line (don't forget to include
access_token in the URL as well), and we will
immediately and synchronously send a "ping" event to the
webhook subscription's target URL.
The HTTP status code that your app returns to us will be displayed as the status field in the response.
This is a one-time notification, and will not be retried if it fails or times out.