using System;

using SendGrid.SmtpApi;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var header = new Header();

        var uniqueArgs = new Dictionary<string, string> 

        {

          { "PostId", "1" },

          { "RecipientUserId", "2"}

        };

​

        header.AddUniqueArgs(uniqueArgs);

​

        var xmstpapiJson = header.JsonString();

        Console.WriteLine(xmstpapiJson);

    }

}