Can not add users - Need help ASAP

Hi,

We just set up a Vultr Jitsi Server. And as admin, I have added my users, but none of them could sign in to set up their meetings.

This is the error I am getting:

And my users are listed when I searched for it.

or: The host ‘xyz.com’ is not listed in the configuration file (or is not enabled).

The user will not be able to log in until this is changed.

I know almost nothing about Linux. What commands do I need to put in so that users are activated correctly?

Thank you so much!

Jing