sometimes the source returns 503 status error due to server issues I think.
ERROR: Unable to download webpage: HTTP Error 503: Service Unavailable (caused by <HTTPError 503: 'Service Unavailable'>); please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; see https://yt-dl.org/update on how to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.
sometimes the source returns 503 status error due to server issues I think.