Authentik frontend calls localhost

[ThomasSteinbinder]

I installed authentik via docker compose on my remote server, as described in the installation guide.
When I try to do the initial setup on "https://auth.myserver.com/if/flow/initial-setup/" I see "Reqest failed, Please try again later". I also see requests to https://localhost:9000/api/v3/root/config/ or wss://localhost:9000/ws/client/ which is blocked. I access the frontend from my local machine and not from the server. I guess the requests should be going to the server? Is there any config that is not mentioned in the docs?
There must be an option to tell authentik its actual address

Any hints appreciated!

It runs behind nginx btw

server {
    listen 80;
    server_name auth.myserver.com;

    return 301 https://auth.myserver.com$request_uri;
}

server {
    listen 443 ssl;
    server_name auth.myserver.com;
    ...
    location / {
        proxy_set_header X-Forwarded-For   $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_pass http://localhost:9000;
    }
}

[ThomasSteinbinder]

okay reading the reverse proxy docs helped... :)