Tested with:
set service dns dynamic interface eth0.203 service custom host-name 'test.vyos.net' set service dns dynamic interface eth0.203 service custom login 'vyos' set service dns dynamic interface eth0.203 service custom password 'vyos' set service dns dynamic interface eth0.203 service custom protocol 'dyndns2' set service dns dynamic interface eth0.203 service custom server 'vyos.io'