GCM push notification when iOS app is in the background

Question

I'm trying to send push notifications to my iOS app with GCM. The app doesn't get the notification when it's in the background but it does when it's in the foreground. I was testing the push notifications with a PHP script also which sends the message directly to the APNS and it's working in the background.

The JSON sent to GCM: (I'm sending it from a rest client for testing)

{
  "to" : "token...",
  "notification" : {
    "title": "GCM TITLE",
    "body" : "FROM GCM",
    "badge": "1",
    "sound": "default"
  }
}

Not working : The userInfo received from GCM in didReceiveRemoteNotification:

Notification received: [aps: {
    alert =     {
        body = "FROM GCM";
        title = "GCM TILE";
    };
    badge = 1;
    sound = default;
}, gcm.message_id: 123...]

Working : The userInfo received when sent from the PHP script (I also added the message_id to the JSON to see if that's the problem)

Notification received: [aps: {
    alert =     {
        body = "FROM PHP";
        title = "PHP TITLE";
    };
    badge = 2;
    sound = default;
}, gcm.message_id: 123...]

I tried adding content_available to the JSON with different combinations but didn't help, the Content-Type and Authorization request headers are also set:

Content-Type:application/json
Authorization:key=... 

Answer 1

In case if someone has the same problem, the solution was for me to add the "priority": "high" to the JSON. This way I get the notifications in the background.

{
  "to" : "token...",
  "priority": "high",
  "notification" : {
    "title": "GCM TITLE",
    "body" : "FROM GCM",
    "badge": "1",
    "sound": "default"
  }
}

Answer 2

To get notification when app is in background i note that we need to add:

"content_available":true // when app in background
"priority":"high" //when app is completely closed not even running in background

 // "content_available":true  ..most important field 

{
"to" : "token...",
 "priority":"high",
 "content_available":true,
 "notification" : {
 "title": "GCM TITLE",
 "body" : "FROM GCM",
 "badge": "1",
 "sound": "default"
  }
}