When i set up a hook Pull Request POST, everything is correct for the pullrequest_created call. But when the hook is called with pullrequest_updated, the id of the pull request is not in the payload. I don't have any other field i can rely on (like the api url for this PR, etc.).
Actually this is blocker bug in the workflow - we can't use the api without this Id.
If you need further details, just ask.