Unable to establish multi user communication

I have installed the latest version of Jitsi on Ubuntu machine. I am unable to have conference for more than 2 people. It is working fine for 2 users.

@damencho Can you please help me in the setup.
Thanks in advance

Follow advance part of quick install guide make sure ports are open on firewall, forwarded if needed to be and public & private address are set to the bridge if behind nat.