Since upgrading to bookworm (from bullseye), I see these failures in my
logs:

  ddclient[1081]: FAILED:    was not updated because protocol <undefined> is not supported.

This is what my /etc/ddclient.conf contains:

  ssl=yes
  protocol=noip
  use=web, web=https://ip-address-reflector.example/
  server=dynupdate.no-ip.com
  login=username
  password='...'
  hostname.dyn.domain.example

I thought the systemd unit file was having problems reading the config file
in /etc/:

  -rw------- 1 root root 268 Feb 14  2022 ddclient.conf

and so I added this in /lib/systemd/system/ddclient.service:

  [Service]
  User=root

but it didn't seem to do anything.

Francois