code 404 (Not Found) at c#

using System;
using System.Threading.Tasks;
using RingCentral;
namespace Call_Ringout
{
    class Program
    {
          const string RECIPIENT = "<ENTER PHONE NUMBER>";
          const string RINGCENTRAL_CLIENTID = "<ENTER CLIENT ID>";
          const string RINGCENTRAL_CLIENTSECRET = "<ENTER CLIENT SECRET>";
          const string RINGCENTRAL_USERNAME = "<YOUR ACCOUNT PHONE NUMBER>";
          const string RINGCENTRAL_PASSWORD = "<YOUR ACCOUNT PASSWORD>";
          const string RINGCENTRAL_EXTENSION = "<YOUR EXTENSION, PROBABLY ";
          static void Main(string[] args)
          {
              call_ringout().Wait();
          }
          static private async Task call_ringout()
          {
              RestClient rc = new RestClient(RINGCENTRAL_CLIENTID, RINGCENTRAL_CLIENTSECRET, false);
              await rc.Authorize(RINGCENTRAL_USERNAME, RINGCENTRAL_EXTENSION, RINGCENTRAL_PASSWORD);
              if (rc.token.access_token.Length > 0)
              {
                  var parameters = new MakeRingOutRequest();
                  parameters.from = new MakeRingOutCallerInfoRequestFrom { phoneNumber = RINGCENTRAL_USERNAME };
                  parameters.to = new MakeRingOutCallerInfoRequestTo {  phoneNumber = RECIPIENT } ;
                  parameters.playPrompt = false;
                  var resp = await rc.Restapi().Account().Extension().RingOut().Post(parameters);
                  Console.WriteLine("Call Placed. Call status" + resp.status.callStatus);
              }
          }
      }
}