Thx for your help, you all. I will check the possibilities!

Got it. I was using the account id with an application key. A more careful reading of the above linked page shows that: So that was the disconnect. Application Key requires Application ID. Account ID requires Master Application Key. When the examples clearly stated ACCOUNT_ID and APPLICATION_KEY

Sadly, Zimbra is an exception.

Edgerouters can now handle custom dynamic dns providers without the need of the script - here is the guide with Cloudflare as the example: https://help.ubnt.com/hc/en-us/articles/204976324