code: def join_group_with_token(self, group_hashtag, group_jid, join_token):
          
          log.info("[+] Trying to join the group '{}' with JID {}".format(group_hashtag, group_jid))
          return self._send_xmpp_element(roster.GroupJoinRequest(group_hashtag, join_token, group_jid))
docs: Tries to join into a specific group, using a cryptographic token that was received earlier from a search
  
          :param group_hashtag: The public hashtag of the group into which to join (like '#Music')
          :param group_jid: The JID of the same group
          :param join_token: a token that can be extracted in the callback on_group_search_response, after calling
                             search_group()