a Problem with POST Request in WebForms ?

Question

I am trying to read API for example like "https://test......." with POST request and Basic authentication . 

the POST request has Body with URL . i should pass url insaid a body to get json data back which i want to convert it into C# object but the Problem that i am getting always the erro 401 or 405 and i cant get the response . 

 my goal is to get the json data back but how could i pass the url which is in Body ? and why i am getting this erros 401,405 . 

for any help i will be happy 

private string LoadHttpPageWithBasicAuthentication()
       {
           //List<WebShopWebTexte> webShopWebTextes = new List<WebShopWebTexte>();
           Uri myUri = new Uri("https://.......");
           WebRequest request = HttpWebRequest.Create(myUri);
           request.Method = WebRequestMethods.Http.Post;

           request.ContentType = "application/json";

           HttpWebRequest httpWebRequest = (HttpWebRequest)request;

           NetworkCredential myNetworkCredential = new NetworkCredential("++++", "++++");

           CredentialCache myCredentialCache = new CredentialCache();
           myCredentialCache.Add(myUri, "Basic", myNetworkCredential);

           httpWebRequest.PreAuthenticate = true;
           httpWebRequest.Credentials = myCredentialCache;

           WebResponse response = request.GetResponse();

           Stream responseStream = response.GetResponseStream();

           StreamReader myStreamReader = new StreamReader(responseStream, Encoding.Default);

           string pageContent = myStreamReader.ReadToEnd();

           responseStream.Close();

           response.Close();

           return pageContent;

       }