RingCentral Voice Call in ASP.NET MVC 4.6.2

Question

I am trying to make voice call on ringCentral in my ASP.NET MVC 4.6.2. I used code from ringCentral documentation regarding C#. But When I try to make a call. It shows "The resource you are looking for (or one of its dependencies) could have been removed" on line: "var resp = await restClient.Restapi().Account().Extension().RingOut().Post(parameters);"

Note: I am trying to make a call from ringCentral Sandbox phone number to my personal phone number in Pakistan. The Code is attached below:

[HttpPost]
public async Task Call_From_RingCentral()
{
    restClient = new RestClient(
    "65ty", //client id
    "12gh", //client secret
    "https://platform.devtest.ringcentral.com"); //server url
    await restClient.Authorize("JWT");
    await call_ringout();
  }

  static private async Task call_ringout()
  {
    var parameters = new MakeRingOutRequest();
    parameters.from = new MakeRingOutCallerInfoRequestFrom
    {
        phoneNumber = Environment.GetEnvironmentVariable("+13232......")
    };
    parameters.to = new MakeRingOutCallerInfoRequestTo
    {
        phoneNumber = Environment.GetEnvironmentVariable("+92300067.....")
    };
    parameters.playPrompt = false;

    var resp = await 
     restClient.Restapi().Account().Extension().RingOut().Post(parameters);
     Console.WriteLine("Call Placed. Call status" + resp.status.callStatus);
   }