docs: def _make_fake_message(self, user_id, page_id, payload):
          """
          Creates a fake message for the given user_id. It contains a postback
          with the given payload.
          """
  
          event = {
              'sender': {
                  'id': user_id,
              },
              'recipient': {
                  'id': page_id,
              },
              'postback': {
                  'payload': ujson.dumps(payload),
              },
          }
  
          return FacebookMessage(event, self, False)