Example of configuration, please look all, there are a lot of changes between NethServer ejabberd configuration, example you use 5223 by default and it is not here:
loglevel: info:
-> https://github.com/processone/ejabberd/commit/e4a8afb15d6c995b294a60ed150b86775e2f6805
OMEMO part, 5223 part, BOSH part, …
Several options need to be in Nethgui/Cockpit…
Warning: Pidgin is the best bad XMPP client, please do not use it.
Computer: Psi/Psi+ is the best with Gajim.