A General purpose rest ApiClient write in C# language for the OneSignal API
PM> Install-Package OneSignal.CSharp.SDK
var client = new OneSignalClient("ZWM3YThlMmQtMzY1NC00ODI1LTlkYjMtMTk3MzI2OTQzMjVh");
var options = new NotificationCreateOptions();
options.AppId = Guid.Parse("af447f99-a469-4fa2-a8aa-435bf449900f");
//options.IncludedSegments = new List<string> { "All" };
options.Contents.Add(LanguageCodes.English, "salam chetori?");
options.IncludedPlayerIds = new List<string>() { "4581a321-9ce5-4201-be19-58e3436834c4" };
var result = client.Notifications.Create(options);
[OneSignal Server API] (https://documentation.onesignal.com/reference)