How to get custom domain working?

Hello! I am trying to set up a custom domain for my Leantime installation, and would appreciate some help.

What I Tried

I used the one command install with docker-compose, except I added LEAN_APP_URL in docker-compose.yml.

git clone https://github.com/Leantime/docker-leantime.git
cd docker-leantime
nano docker-compose.yml
docker-compose up -d
version: '3.3'

services:
   db:
     image: mysql:5.7
     container_name: mysql_leantime
     volumes:
       - db_data:/var/lib/mysql
     restart: always
     environment:
         MYSQL_ROOT_PASSWORD: '321.qwerty'
         MYSQL_DATABASE: 'leantime'
         MYSQL_USER: 'admin'
         MYSQL_PASSWORD: '321.qwerty'
     ports:
       - "3306:3306"
     command: --character-set-server=utf8 --collation-server=utf8_unicode_ci
   web:
     image: leantime/leantime:latest
     container_name: leantime
     environment:
         LEAN_DB_HOST: 'mysql_leantime'
         LEAN_DB_USER: 'admin'
         LEAN_DB_PASSWORD: '321.qwerty'
         LEAN_DB_DATABASE: 'leantime'
         LEAN_APP_URL: 'https://subdomain.example.com'
     ports:
       - "9000:9000"
       - "80:80"
     depends_on:
       - db
volumes:
    db_data: {}

With this setup, I get the following behavior:

http://xx.xx.xx.xx redirects to https://subdomain.example.com/install, which does not load (ERR_CONNECTION_TIMED_OUT)
http://xx.xx.xx.xx/install shows the installation page, but the CSS and JS is not loaded properly. On filling out the form, I go to https://subdomain.example.com/install, which again does not load.