os-ddclient generates empty ddclient.conf although account exists in config.xml/json

I can reproduce an issue with os-ddclient on OPNsense when using Infomaniak DynDNS.

What works:

• The DynDNS account is correctly stored in /conf/config.xml
• The account is correctly rendered into /usr/local/etc/ddclient.json
• A manual ddclient test with the same Infomaniak credentials works successfully

What does not work:

• /usr/local/etc/ddclient.conf only contains the header lines:
  syslog=yes
  pid=/var/run/ddclient.pid
• No actual account configuration is written to ddclient.conf
• service ddclient_opn starts and stays running, but has no usable account configuration

My test case:

• service: custom
• protocol: dyndns2
• server: infomaniak.com
• hostname:
• username/password: Infomaniak DynDNS credentials

Relevant observation:

• Manual ddclient works with:
  protocol=dyndns2
  server=infomaniak.com
  use=ip
  ip=
  login=
  password=
  

This suggests the problem is not Infomaniak itself, but the OPNsense os-ddclient template/runtime generation, because:

• config.xml = OK
• ddclient.json = OK
• ddclient.conf = missing account entries

Opnsense: 26.1.9
os-ddclient 1.31

Start by tracing how the account moves from /conf/config.xml and /usr/local/etc/ddclient.json into /usr/local/etc/ddclient.conf, then reproduce the Infomaniak custom dyndns2 case with service ddclient_opn. Done means the generated ddclient.conf contains the usable account entries and the service runs with that configuration.