Token Suscripcion not response

[Mxater]

Hello, I using the lib, but when suscribe a client to a topic, this dont reply any.

$response=$client->addTopicSubscription('GROUP' . $user->getGrupo()->getId(), [$user->getToken()]);

$user->getGrupo()->getId()=2 [$user->getToken()] = [dGi1kW52if8:APA91bFQ3LfgDr6ogK_2412Vfwytyn_q....]

I get this reply

Response Code = 200 Response Reply = {"results":[{}]}