aps {
       content-available: 1
       alert: {...}
     }

aps {
      content-available: 0
      alert: {...}
    }

application.registerForRemoteNotifications() // This does NOT require user permission.

UNUserNotificationCenter.current().requestAuthorization([.alert, .badge, .sound]) { (granted, error) in

    guard error == nil else {
        //Display Error.. Handle Error.. etc..
        return
    }

    if granted {
        //Do stuff here..

        //Register for RemoteNotifications. Your Remote Notifications can display alerts now :)
        application.registerForRemoteNotifications()
    }
    else {
        //Handle user denying permissions..
    }
}

{
    "aps" : {
        "content-available" : 1
    },
    "acme1" : "bar",
    "acme2" : 42
}

"aps" : {
        "alert" : "You got your emails.",
        "badge" : 9,
        "sound" : "bingbong.aiff"
    },
    "acme1" : "bar",
    "acme2" : 42
}