when trying to use Collabora in Nextcloud I get 404 Error when clicking on a document.

When trying to use Collabora in Nextcloud I get 404 Error when clicking on a document. Both systems are on local LAN. I can ping the Hostname of each system from both systems. Collabora/CODE is installed on a seperate Ubuntu System in a docker. I am assuming it has something to do with the Proxy and or Docker since Nextcloud and Collabora are on seperate boxes.

You're probably going to have to check some of your logs to figure out what's going on. I'd look at the Apache (or NGINX, whatever you're using) logs, and the Collabora/loolwsd log in journalctl.