set content-available using moon apns

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C#

iOS

referring to this link : http://www.objc.io/issue-5/multitasking.html i can now send a silent push notification on ios by setting content-available=1

i'm using moon apns on c# to send the push notification but i can not find this property to send a silent push (i'm using a development certificate)

below is my code :

string p12File = "test.p12";
string p12FilePassword = "1234";
bool sandbox = false;
var push = new PushNotification(sandbox, p12File, p12FilePassword);
NotificationPayload payload1;
payload1 = new NotificationPayload(testDeviceToken, message, 0, "Silence.m4R");
payload1.AddCustom("message", "HIDDEN");
var notificationList = new List<NotificationPayload>() { payload1 };
var rejected = push.SendToApple(notificationList);
foreach (var item in rejected)
{
   return false;
}

any idea how can send this using moon apns :

{
"aps" : {
    "content-available" : 1
},
"content-id" : 42
}