Problem with getting IOS device token.

I'm trying to use the Unity API get IOS device token to register push notification. The difficulties I found that the UnityEngine.iOS.NotificationServices.deviceToken always throw me null value.

When the app calling RegisterForNotifications, xcode did throw the token back with result below.
2016-04-26 17:52:56.445 ****[869:1651521] [NotifyEventListener] Method=DidRegisterRemoteNotification, Message=38db43d982215985afd4ce149227eec4b4b260196fda56df13d246c95b76d8b6

But after that comes to...

Problem with getting IOS device token.