Nothing fancy. I just used my SIP account name (a number provided by my
SIP provider that appears under 'SIP-Kennung' in jitsi)
and my password.
I can't see anything like 'domain' for configuration....
I'm asking because the logs show "123456 (personal-voip) (SIP)" as an
account, but this should be "firstname.lastname@example.org (SIP)". So my guess was
that you entered "123456 (personal-voip)" into SIP-Kennung.
On the other hand the logs you sent me privately show that the basic setup
is working, but Jitsi's reply to the incoming call never reaches the
provider. Then the account disconnects and reconnects to a different server
of your provider.