SmsController.cs

using System.Web.Mvc;
using Twilio.TwiML;
using Twilio.TwiML.Mvc;

namespace ReceiveSms.Controllers
{
    public class SmsController : TwilioController
    {
        // POST: Sms
        [HttpPost] 
        public ActionResult Index(string From, string Body)
        {
            var twiml = new TwilioResponse();
            var message = twiml.Message($"Hello {From}. You said {Body}");
            return TwiML(message);
        }
    }
}