Ionic Firebase ios unable to subscribe to topic

I have a Ionic app where in I want to be able to push notifications using Firebase, we have used FCM library for the same. The notifications work seamlessly on android, however on the iOS I am facing the challenge that the device is not able to subscribe to the topic and hence not getting any notifications. Steps followed:

1. On the apple developer account created an APP ID.
2. Created a profile and loaded it on my mac
3. Created a key uploaded it and then generated a .p12 key for it(certificate).
4. Uploaded this key on the firebase app for ios under my project.
5. Run my app on the device.
6. Token is generated but cant subscribe to topic.

Below are the excerpts from XCode logs:

2018-11-21 16:48:17.808: <FIRInstanceID/WARNING> Failed to fetch APNS token Error Domain=com.firebase.iid Code=1001 "(null)"
2018-11-21 16:48:17.810: <FIRMessaging/WARNING> FIRMessaging AppDelegate proxy enabled, will swizzle app delegate remote notification receiver handlers. Add "FirebaseAppDelegateProxyEnabled" to your Info.plist and set it to NO

and:

2018-11-21 16:48:28.629527+0530 safe-school-app[3421:1163750] InstanceID token: frO-ryN8Yu8:APA91bG0WkMaAxAAVIsW33A21kvv8n27ehjcPOw3QunOuN0gylfK4EROB8JkhInJ7mnGoY68Jqf8YjGE6E6FYUq7H38qa5c3axW9LnScw0iOLtZ52EQZn3DR3SLC_7RTqrEwRNvbUtbX
2018-11-21 16:48:29.404: <FIRMessaging/WARNING> Failed to subscribe to topic Error Domain=com.google.fcm Code=5 "(null)"

I have tried FirebaseAppDelegateProxyEnabled to both be Yes and No.

Any help in this regard will be highly appreciated.

-Vaibhav

Presumable it seems that these are warnings, i tried it building using the "Legacy Build System" and the firebase notifications work just fine.