Apparently, the Request: "/nic/update?" fails.
The System Log shows these two events,
06/01/2018 01:13:31 PM System Event /var/ddnsd.cfg:6: no such option 'Ts'
06/01/2018 01:13:31 PM System Event Parse error in /var/ddnsd.cfg

I just now setup DDNS using api.dynu.com using the instructions at https://www.dynu.com/DynamicDNS/IPUpdateClient/Zyxel-C1100Z,
and the lines below
"Dynamic DNS Reporting
Reported Address Date Time Report Status"
are empty after rebooting ZYXEL.

Complete System Log:
06/01/2018 01:13:20 PM System Event BusyBox v1.17.2
06/01/2018 01:13:20 PM System Event IPSEC SPU: SUCCEEDED
06/01/2018 01:13:20 PM DHCP ebt_dhcpopt registered
06/01/2018 01:13:31 PM System Event /var/ddnsd.cfg:6: no such option 'Ts'
06/01/2018 01:13:31 PM System Event Parse error in /var/ddnsd.cfg
06/01/2018 01:13:33 PM DSL Link Line 0: xDSL G.994 training
06/01/2018 01:13:41 PM Ethernet eth3 (switch port: 1) Link UP 1000 mbps full duplex
06/01/2018 01:13:48 PM DSL Link Line 0: ADSL G.992 started
06/01/2018 01:13:53 PM DSL Link Line 0: ADSL G.992 channel analysis
06/01/2018 01:13:56 PM Ethernet eth0 (switch port: 4) Link UP 100 mbps full duplex
06/01/2018 01:14:01 PM DSL Link Line 0: ADSL link up, Bearer 0, us=891, ds=15870
06/01/2018 01:14:29 PM PPP Link PPP sent PADI.
06/01/2018 01:14:29 PM PPP Link PPP PADO received.
06/01/2018 01:14:29 PM PPP Link PPP session established.
06/01/2018 01:14:32 PM PPP Link PPP LCP UP.
06/01/2018 01:14:32 PM PPP Link PPP Received valid IP address from server. Connection UP.