The data deletion callback is called whenever an app user removes your app and requests that you delete their data. Your app users can do this by going to their Facebook profile and clicking the Send Request button on the Settings & Privacy > Settings > Apps and Websites page.
This generates a POST with a signed request that is sent to your app. The signed request contains an app-scoped ID identifying the user making the request. For an example of how to parse the request and the structure of the parsed request, see the following section.
In response to the user request, you should acknowledge receiving a user data deletion request through the technical means we provide, and provide a link and a confirmation number. The link and confirmation number must give the user access to a human-readable explanation of the status of their request, including a legitimate justification for any refusal to delete (where legitimate will vary based on jurisdiction and our case-by-case interpretation of our policy as it relates to their stated reasons).