C sharp - Subir fichero a servidor php desde C#

try

            {

                ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };

                ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

                ServicePointManager.Expect100Continue = true;

                ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls

                       | SecurityProtocolType.Tls11

                       | SecurityProtocolType.Tls12

                       | SecurityProtocolType.Ssl3;

                //System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;

                using (WebClient client = new WebClient())

                {

                    //System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3;// Tls12;

                    client.Headers.Add("Accept-Version", "2.0");

                    string filePath = @"C:\PDF\a.jpg";

                    var serverPath = new Uri(@"https://miservidor/Downloads/upload.php");

                    client.UploadFile(serverPath, filePath);

                }

                Application.Exit();

            }

            catch (Exception err)

            {

                MessageBox.Show(err.Message);

            }

<?php

$uploads_dir = './img'; //Directory to save the file that comes from client application.

if ($_FILES["file"]["error"] == UPLOAD_ERR_OK) {

    $tmp_name = $_FILES["file"]["tmp_name"];

    $name = $_FILES["file"]["name"];

    move_uploaded_file($tmp_name, "$uploads_dir/$name");

}

?>