I am trying to implement Twilio voice calls in C#.
I have the following code which initiate a call.

        var accoutnSid = "XXXXXXXXXXXXX";
        var authToken = "XXXXXXXXXXXXX";
        TwilioClient.Init(accoutnSid, authToken);
        var to = new PhoneNumber("tonumber");
        var from = new PhoneNumber("fromnumber");
        var response = new VoiceResponse();
        response.Say("Hello, Please speak");
        response.Gather(
            input: new []{Gather.InputEnum.Speech}.ToList(), 
            timeout: 2, 
            action: new Uri("https://mywebapi.com/version/v0/routecalls/twilioresponse"), 
            method: Twilio.Http.HttpMethod.Post);
        response.Say("Thanks for your input");
        var call = CallResource.Create(to: to, from: from, twiml: response.ToString());

When the user is done talking, per Twilio documentation below end point is called
https://mywebapi.com/version/v0/routecalls/twilioresponse.

The code at the end point is below.

using Microsoft.AspNetCore.Mvc;
using Twilio.AspNet.Common;
using Twilio.AspNet.Core;
using Twilio.TwiML;

namespace webapi.Controllers;
[ApiController]
public class TwilioCallsController : TwilioController
{
    public TwiMLResult twilioresponse(VoiceRequest request)
    {
        Console.WriteLine(request.ToString());
        var response = new VoiceResponse();
        response.Say("You selected sales. Good for you!");
        return TwiML(response);
    }
}

The first part of the setup works fine, but when the user is done talking and I call the API end point, I get the following error at the API end point. 415 Unsupported Media Type
Could someone please let me know what am i doing wring.