503 Error (Service Unavailable) after new installation

You’re using the Setup from the zammad-docker-compose repo, right?

This seems to be the log of the scheduler-container.
More interesting would be the output of the init container and the nginx container.

I installed the compose stack via Portainer (what I guess would be a good way for you too, since it makes the handling a bit easier).
For me it’s docker logs zammadgit_zammad-nginx-1 where “zammadgit” is the stack-prefix.

Maybe this helps you