rjkunde
Do other popups and help tips work? If not then AJAX is not working properly and you need to figure that out. If it’s just this particular popup then you need to check all logs (general server logs, webserver error logs, PHP error logs, MySQL/MariaDB error logs, osTicket System Logs, Browser Console logs, etc.) for any related errors. 500 errors are very generic and hint at a deeper issue which should be logged somewhere. Check your PHP configurations to ensure you have logging enabled and have a log file set, for Apache do the same, and for MySQL do the same.
Cheers.