On Premise - Problem starting the provided docker-compose.yml

Jet admin was so kind to provide an access token, so I could host Jet Admin myself.
However, I tried to start with the default configuration provided.

Within the docker-compose.yml the part for starting backend_nginx looks as following:

  restart: always
  image: registry.gitlab.com/jet-admin/jet-onpremise:backend_nginx-${BUILD_NAME}
  - backend:backend
  - "8000"
  - backend:/shared
  - media:/application/media
  command: [
    "bash", "/usr/local/bin/wait-for-it.sh", "backend:1718", "--",
    "bash", "/usr/local/bin/entrypoint.sh"

Docker sends an error message, that the container can’t start, because the scripts are not found. I also logged into the container an checked: The scripts are not provided.
Also “bash” is not available in this image.

For the first step I commented the command execution, than the container starts. But with this I can’t get the whole application to run. It is possible to access the login page from the frontend, but then any try to setup an account is not forwarded to the backend.
Jet Admin tells me, that there is a network problem.

Did anybody experience a similar problem?