The Create/Update Callback process is designed to allow you a simple and programatic method to create or update your current callback URL used with the iFrame solution.
There are two callbacks that you can configure:
callback - the callback will fire to this endpoint on initial document submission
callback_manual_review - this callback will fire on any additional manual review status changes.
There is also an option to not use the callbacks at all and instead use the User Status API method to fetch the result. If you decide to use this method for either case above just leave your callback endpoint(s) empty.