Get the unseen (new) thread list

        :return: List of unseen thread ids
        :rtype: list
        :raises: FBchatException if request failed

def fetchUnseen(self):
        """
        Get the unseen (new) thread list

        :return: List of unseen thread ids
        :rtype: list
        :raises: FBchatException if request failed
        """
        j = self._post(
            self.req_url.UNSEEN_THREADS, None, fix_request=True, as_json=True
        )

        payload = j["payload"]["unseen_thread_fbids"][0]
        return payload["thread_fbids"] + payload["other_user_fbids"]