How to update DNS via URL?

Josathome

I have a Zyxel account (on https://mycloud.zyxel.com)  incl username, password and hostname (xxxxx.zyxel.me), incl dynamic DNS functionality. I want to use this to keep public IP of my network updated. In the set-up of my Tomato router I have the option to do this via URL. 

My question is how to do (I guess all details (username, etc) should be included... )
Acc “Tomato forum” the API that Zyxel uses, must be known.... (whatever this means)...