Can't make update DDNS on Zyxel Zywall USG 50.
Got error:
DDNS Dynu_1 has an unknown error: HTTP/1.1 200 OK\x0d\x0aDate: Mon, 07 May 2018 22:8:6 GMT\x0d\x0aServer: Dynu Web Server\x0d\x0aX-Powered-B

With both Dynu Basic/Premium. Password and domain is correct, no login option at that router.
Is that router still supported?

Zyxel Zywall USG 50 worked for me. Are you using any special characters in the password? Try changing into a password without any special characters.