Can't join my Forge 1.7.10 server

[teoba]

Hi there!
I have installed a Forge 1.7.10 server because I want to use the Lord Of The Rings mod. I'm running Ubuntu 20.04 LTS and OpenJDK 8 on a cloud server by Hetzner. As the title already says, the problem I have is that I am not able to join my server. I have opened the port already (sudo ufw allow 25565), but it still doesn't work. The command "netstat -tulpn | grep java" returns the following:

tcp6       0      0 :::25565                :::*                    LISTEN      14932/java          

This is why I suspect that Forge is only running in the local network but not publicly.

Does someone have a clue why this occurs and how to fix this?