does not connect to the site to find out the version [duplicate]

Good day, the question is, I uploaded a text document to my site in a separate folder in which I store the version of the application, but when I connect to it, it gives me an error ..

Error: The underlying connection is closed. Failed to establish trust for secure channel.

        try
        {
            using (var client = new WebClient())
            using (var stream = client.OpenRead(link_version)) // link in check
            using (var reader = new StreamReader(stream))
            {
                ClientInfo.activ_version_launcher_site = reader.ReadToEnd();
                //=========//
                if (version_launcher == ClientInfo.activ_version_launcher_site)
                {
                    Status = LauncherStatus.Launcher_Ready;
                    Check_Default_Launcher(sender, e);
                }
                else
                {
                    Status = LauncherStatus.Launcher_update_ready;
                    Button_update.Width = 185;
                    Button_update.Height = 30;
                    Button_update.Opacity = 1;
                    ClientInfo.for_check_old_version_Setup = true;
                    StockSaveAll_parametr();
                }
            }
        }
        catch (Exception ex)
        {
            Status = LauncherStatus.Launcher_update_download_error;

            ErrorLauncher.ErrorMessager = ex.Message;

            var closeds = new LauncherError();
            img_bg.Opacity = 0.3;
            closeds.Owner = this;
            ApplyEffect(this);
            closeds.ShowDialog();
            ClearEffect(this);
             
        }