Connect Nextcloud Docker container to Mysql plugin

Hi, I've been reading some posts in the forum, relative to this matter, but couldn't find any solution to my problem on them. Like many people I've installed nextcloud in a docker container following the "Techno Dad Life" youtube tutorial, this one https://youtu.be/PKsq7k2pwsI

The thing is, after try nextcloud for some days, once I reboot the server, the database in the docker container starts to fail.
Therefore I decided to use the OMV MySql plugin instead.

I deleted the docker containers and I started a new one for nextcloud, so I can have a clean new installation. I installed the Mysql plugin, created the database, the user and so on, and I can log in mysql with both root and nextclouddbuser using the web interface,
The problem is when I try to create the admin account in the nextcloud first setup page, I still getting always the message

Error while trying to create admin user: Failed to connect to the database: An exception occured in driver: SQLSTATE[HY000] [2002] Connection refused

it doesn't matter if I try to connect to the database via root or via the new db user, and I'm wondering if there is some "special" config I'm missing to connect with the mysql plugin instead of a docker container.

Just as info, since in the youtube tutorial both the database and the nextcloud are docker containers, the guy doesn't set the PUID nor the PGID on the nexcloud container, but since I need to communicate with the plugin I'm doing it in my container.

Can someone throw some light here, I've been trying stuff for a couple of weeks now, and can't find a solution.

Thanks in advance!
Sime