Hi @manu
The add button should send “wp-admin/admin-ajax.php” POST request to the server instead of the current URL. Maybe there’s something in your site that prevents it. Could you please try to reproduce the issue on one of the WordPress’ stock themes (like Twenty Sixteen) with other plugins deactivated? If it disappears, then you can activate the theme and plugins one by one to see which one causes the issue.
Thanks 🙂
