Even though the issue is not yours to troubleshoot or resolve, there are a few things you can do:

Retry the web page by clicking the refresh/reload button or trying the URL from the address bar again.
Even though the 500 Internal Server Error is reporting a general error on the web site's servers and not your computer, the server error may only be temporary.
Trying the page again will often be successful.

If you can't wait any longer for the problem to be resolved or if you'd like to help out,
you may want to attempt to contact our webmaster at portal@xplorewealth.com.au