OneSignal.PushNotification.API

Sends push notifications to specific mobile devices/device via OneSignal web API.

You can use it like this:

            Notification myNotification = new Notification();
            myNotification.contents = "HEELO FROM PUSH NOTIFICATION!";
            myNotification.small_icon = "icon.png";
            myNotification.include_player_ids = new List<string> { "OneSignal_playerid_fordevice","Another_onesignal_playerid" };
            myNotification.Send();

It's Easy You can find a sample here: Sending Push Notifications from API | enisnecipoglu.com