The thing is that the docker xibo-cms connect to tcp://xibo-cms:50001. But in the plesk docker container the environment does not allow to connect to tcp://xibo-cms:50001. Only IP. So in PHPmyadmin i enabled the settings of the private adress and that solved the problem for now. THe connection from the player to XMR always worked. Because the docker container exposure to the outside is fine.
Thnx for the reply!