Cannot subscribe to topic: /topics/test with token: (null)

Editor: Xcode 8.3.2
Device: iPhone 5s ( iOS 10.3.2 )
Language: Objective-C

Solutions tried before raising this issue

1. Clean Xcode, delete App and reinstall.
2. Subscribing to topic after some delay and after FCM token is received.
3. Updated PODS to latest version.
4. Only subscribing to ONE topic.
5. /topics/ is prefixed.

NOTE

1. The subscription works perfectly fine in Android and immediately gets appeared in Firebase console drop down.
2. I am able to get FCM token and receive push notification on iOS when sent using Bundle ID(APP).

CODE
[[FIRMessaging messaging] subscribeToTopic:@"/topics/test"];

[morganchen12]

What version of Firebase are you using? You shouldn't have to prefix topics with /topics/.

Thanks. Its working now... 👍
I was unable to start debugger. So could not capture the exact error. #471 solved my debugging problem.

Changed the code from
[[FIRMessaging messaging] subscribeToTopic:@"/topics/test"];
to
[[FIRMessaging messaging] subscribeToTopic:@"test"];

Initially I get following error:
[Firebase/Messaging][I-FCM002010] Cannot subscribe to topic: test with token: (null)
But later I get :
Topic subscription request: sender=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

And now i can receive push notification on a topic on iOS as well.
Happy to close.