Why does telegram api communication error occur?

Question

C++ / C#

what is the error of this request, why is there no connection with the server if I do everything right?

{
                    string response = c.DownloadString(
                        "https://api.telegram.org/bot" + token + "/sendMessage" +
                        "?chat_id=" + chatid +
                        "&text=" + text +
                        "&parse_mode=Markdown" +
                        "&disable_web_page_preview=True"
                    );
                    return false;
                }