How to connect Nextcloud Snap 24.0.6 with own Collabora Online Code server

I am not an -IT pro and I would like to ask for help.
This is the configuration of my Home lab server running on Proxmox.

  1. VM01 - Ubuntu server 22.04 + NGINX Proxy server in docker
  2. VM02 - Ubuntu server 22.04 + Nextcloud SNAP 24.0.6snap1 + Collabora Online Code server in docker on port 9980

There are 2 subdomains

The Nextcloud SNAP subdomain works fine. The Collabora Online server is also reachable with the status OK (as shown in the tutorial).

I installed the Nextcloud office app.
Here comes my issue.
Nextcloud office app settings - Use your own server
I put it there -
After 20 sec I receive - Could not establish connection to the Collabora Online server.

I fight with the issue for more than a week.
What am I missing?

Could you be so kind and would you help me solve the issue?
Thank you for your answer.

sorry for late reply I just found your post today.

It’s hard to say why your NC doesn’t reach CODE server as didn’t add any useful logs and configs (Nextcloud, reverse proxy, CODE), please double check

it shows basic troubleshooting steps for each involved component. used curl commands show issues like DNS or certificate issues in deeper details than you see in Web UI of Nextcloud…

here you will find some more references what others experience in similar setups.