Hi , We were following these links to add push notification to our cross platform project (IOS and Android).
https://docs.microsoft.com/en-us/gaming/playfab/features/engagement/push-notifications/quickstart
and
We were able to easily setup for Android it worked very well with FCM.
But when we built the project for IOS using Unity's Package for Push notification. (As FCM is not supported for IOS)
https://docs.unity3d.com/Packages/com.unity.mobile.notifications@1.2/manual/index.html
----------------------------------------------------------Side Note------------------------------------------------------------
We also use this plugin because UnityEngine.iOS.NotificationServices.deviceToken was always null even after 3 seconds after calling UnityEngine.iOS.NotificationServices.RegisterForNotifications.
And having no proper callback we thought was not reliable any way to poll for the deviceToken, while not knowing whether RegisterForNotification was successful or not.
----------------------------------------------------------End of Side Note----------------------------------------------------
Then we ran into problem mentioned here
After that we were able to remove Firebase Messaging while building to IOS platform, even then we are facing same problem mentioned in above link.
But note that we are able to get notification on IOS device, via some service like
https://www.apnstester.com/apns/
Which makes us believe this might be a bug with Cross-platform message routing (PlayFab via Amazon Simple Notification Service [SNS]). As mentioned in Quickstart.