Lizmap Installation with URL prefix

I am trying to install Lizmap on a server that runs on a portal:

portal.domain.com

The server itself runs on the portal with a prefix(?) added to the url that the server is unaware of to my understanding.

portal.domain.com/prefix

So when I install Lizmap on the server I can access the landing page (no css) but any generated links will point to portal.domain.com/lizmap.

I did not find any solution to this problem.

How can I include this prefix in the installation of lizmap?