code: def set_webhook_handler(self, scope, callback):
          
          scope = scope.lower()
  
          if scope == 'after_send':
              self._after_send = callback
              return
  
          if scope not in Page.WEBHOOK_ENDPOINTS:
              raise ValueError("The 'scope' argument must be one of {}.".format(Page.WEBHOOK_ENDPOINTS))
  
          self._webhook_handlers[scope] = callback
docs: Allows adding a webhook_handler as an alternative to the decorators