it is not happy with "http://..."
change that to "https://..." and it works fine with you php script.
"https://www.zvornik24.info/potd/update.php?ver=2"
without the "s" it was showing an error in the preview window, up in the top right corner - if you click on that and gave it permission to access unsafe scripts, it then started working.
but with the "s" it works every time.