static void Main(string[] args)
        {
            var service = OneSignalNotificationService.GetInstance();

            var heading  = "Header";
            var contents = "Your message contents";

            //For specific devices
            var devicesList = new List <string> {
                "User1 Device Id", "User2 Device Id"
            };

            //For All devices
            //var devicesList = new List<string> { "All" };

            var result = service.CreateNotification(heading, contents, devicesList);

            //Delivery Id
            Console.WriteLine(result.Id);

            //Recipients count
            Console.WriteLine(result.Recipients);

            Console.ReadKey();
        }
 /// <summary>
 /// Method for the get instance of service with singleton pattern
 /// </summary>
 public static OneSignalNotificationService GetInstance()
 {
     if (_oneSignalService == null)
     {
         _oneSignalService = new OneSignalNotificationService();
     }
     return(_oneSignalService);
 }