Can't acces jupyterlab

HI,

I try to make jupyterlab lite work but without success, the page remains blank or with an error message:

The connection was reset or IPLAN took too long to respond.

here is what I have in configuration.yaml:

  jupyterlab:
    title: JupyterLab
    url: http://IPLAN:7777
    icon: mdi:flask

and config add-on

github_access_token: gitub_token
ssl: false
certfile: fullchain.pem
keyfile: privkey.pem
system_packages:
  - ffmpeg
init_commands:
  - pip install virtualenv
  - pip install yamllint

The way is this:
internet -> firewall -> main server -> hassio server

the firewall redirects ports 80,443 and 7777 to the main server.
on the main server, nginx redirects the domain hassio.tld.fr to the internal hassio server.

but how do I redirect port 7777 in nginx so that hassio can actually give me access to jupiterlab.

thanks for your ideas