UniFi OS Server 5.0.6 - Apache reverse proxy

Today I installed my first Inifi OS Server version 5.0.6 and failed at the reverse proxy with Apache.

I installed the server using the GUI installation wizard and then wanted to install Apache as a reverse proxy. Since then, I no longer have access to the GUI and only get error messages in my browser.

Is there one who has allready configured apache as a reverse proxy in front of an Unifi OS Server 5 and can share his apache configuration that is working, please?

None of the sources I have found so far have worked. :confused:

Thx
Andy