Community Document Server with Docker Compose - Onlyoffice Nextcloud

Hallo to all of you, I’m really new to Docker and Docker Compose and making first steps in installing different containers. As the most of them works fine, I have a problem that I can’t go on and it would be really nice someone could answer me about my problem.

Try to tell in short sentences:

I installed nextcloud with docker compose; everything works fine.

I installed Community Document Server in Apps inside nextcloud, to use it with Onlyoffice. This did not work for me! I get an undefined error message when trying to open a file.

I try to install Community Document Server in a separate Docker container, using this Compose commands:

image: onlyoffice/documentserver:latest
container_name: onlyoffice-document-server
  - nextcloud_network
  - ./document_data:/var/www/onlyoffice/Data
  - ./document_log:/var/log/onlyoffice
  - ./document_lib:/var/lib/onlyoffice
  - ./document_db:/var/lib/postgresql
stdin_open: true
tty: true
  - '80'
  - '443'
restart: unless-stopped

The container is installed and has own IP.
My problem: What to do, that I can connect in Nextcloud - Settings - Onlyoffice to use the Document Server? What is the service address?