404 Resource Not Found error when retrieving senders with Managing Senders (REST API) sample code

I would appreciate some help--I am trying out the sample Managing Senders (REST API) code--I just want to retrieve senders--and I'm getting {"messageKey":"http.status.404","message":"Resource Not Found","code":404,"name":"Resource Not Found"}

Here's the code I'm using;

using System;
using System.Diagnostics;
using System.IO;
using System.Net;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Text;

namespace senders
{
    public class managing_senders
    {
        public static void Main(string[] args)
        {

            string apiKey = "my api key here";
            string url = "https://sandbox.esignlive.com/api";

            HttpClient myClient = new HttpClient();
            myClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", apiKey);
            myClient.DefaultRequestHeaders.Add("Accept", "application/json");

            //retrieve sender
            var response = myClient.GetAsync(new Uri(url) + "account/senders?from=0&to=10").Result;
            Debug.WriteLine(response.Content.ReadAsStringAsync().Result);

        }
    }
}

Thanks.