using System;

using Newtonsoft.Json.Linq;

using System.IO;

using System.Text;

​

namespace Demo

{

    public class Program

    {

        public static void Main(string[] args)

        {

            var json = "\uFEFF{ \"invoiceId\": 123456 }";

            // works

            Console.WriteLine("works:");

            using (var stream = new MemoryStream(Encoding.UTF8.GetBytes(json)))

            using (var reader = new StreamReader(stream))

            {

               var requestBody = reader.ReadToEnd(); 

               var parsed1 = JObject.Parse(requestBody);

                Console.WriteLine(parsed1["invoiceId"]);

            }

            // fails

            Console.WriteLine("fails:");

            var parsed2 = JObject.Parse(json);

            Console.WriteLine(parsed2["invoiceId"]);

        }

    }

}