Rapaport Prices HTTP POST with WebClient

string URL = "FILE_URL_PATH";
WebClient webClient = new WebClient();

System.Collections.Specialized.NameValueCollection formData = new System.Collections.Specialized.NameValueCollection();
formData["Username"] = "myusername";
formData["Password"] = "mypassword";
byte[] responseBytes = webClient.UploadValues(URL, "POST", formData);
string Result = Encoding.UTF8.GetString(responseBytes);