LinuxServer/unifi-controller - Container is running but no web access

Hi All,
I installed the latest armhf LinuxServer/unifi-controller in a docker container on a rasp 3b Plus. In Portainer I can see that the container is running and that it has published the proper port 8443. However, I can’t get access via the web ui -> “This combination of host and port requires TLS”. Using https it returns: " … the website sent back unusual and incorrect credentials …".
Any ideas what went wrong?