billing.mydomain.com is currently unable to handle this request. HTTP ERROR 500

mxtoolbox DNS lookup for virtualmin sub server…

A:billing.mydomain.com points to correct ip address for my google cloud instance.

previewing the website from link in virtualmin displays the website.

browsing to website url http:billing.mydomain.com produces the above error.

whmcs is currently in public_html/whmcs/.

instead of moving whmcs up one level (which is a bit of work), is there a way that i can simply tell the webserver to serve up the index page that is in public_html/whmcs/ thus i imagine resolving this issue? can i change the options directive?

Server logs…

[Tue Sep 25 22:27:41.016049 2018] [autoindex:error] [pid 9365:tid 139658302318336] [client xx.xxx.0.4:35560] AH01276: Cannot serve directory /home/domain/domains/billing.mydomain.com/public_html/: No matching DirectoryIndex (index.html,index.htm,index.php,index.php4,index.php5) found, and server-generated directory index forbidden by Options directive

Why not just change the document root for that site to be in the directory want? Or are you going to host other content in the public_html directory?

Virtualmin->[site]->Server Configuration->Website options->Website documents sub-directory->public_html/whmcs