Hi, @timowevel
Got it. The way I understand here is that you are unable to access your Jitsi after you set up Mattermost in which the subdomain meet.timo.com (as an example) redirects to mattermost.timo.com.
Mattermost works and the issue now is that you cannot access Jitsi that is hosted on your end.
How did you configure Mattermost to point to the same server? Which documentation that you referred to? At this point, I am trying to work backwards to find out which step during the deployment of Mattermost that is causing this problem.