Support for domains and certificates is disabled. Ask your system's administrator to enable it

Hello, it’s my first time here. :wink:
I have GitLab CE 13.8.2 and have installed GitLab Pages with a Wildcard-Domain and a second IP address. After a lot of different configurations, I now have pages with an external nginx and it works for one project and one sub-domain. But now for all projects I get “Support for domains and certificates is disabled. Ask your …”, at the configuration for pages.
What is the reason for this message, where is the button for enable, or what is wrong with my config?
Thanks.