Try it and report back. The guide is for domain not URL. I believe URL proxy pass need to be at openmediavault-webui.d/ folder
subzero, when I do this:
ln –s /etc/nginx/sites-available/multi_host /etc/nginx/sites-enabled/multi_host
Which is in your guide I get this result:
ln: target ”/etc/nginx/sites-enabled/multi_host” is not a folder
(I translated this, so maybe saying something else in correct english).