Running Nginx docker

[viviwill]

Hi guys, new here
Really can't get this to work.

I have a docker django + gunicorn + nginx setup.
In docker-compose, for nginx I have:

nginx:
  build: ./nginx
  ports:
    - 1337:85
  volumes:
    - ./staticfiles:/static/
  depends_on:
    - web

In nginx.conf I have it listen to 85 as well.
I did this base on my understanding that I need to avoid port 80, as synology itself is running nginx as reverse proxy.

With above setup, everything work 100% locally, staticfiles are loading and all with localhost:1337
But .... if I open port 1337 in control panel => external access. It failed.

For my other web app without the Nginx server, I can go in External Access => create => built in application => docker and open router port and access remotely without any problems. But not this one.

Any tips?
Thank you in advance.