I found many of the Windows Clients no longer work (December 2021) yet a URL string works just fine.
My solution was to create a Windows task.
Create a task scheduler that runs once an hour on Windows machines:
Under ACTION use: Start program - powershell.exe
Parameters: -Command “Invoke-WebRequest https://ipv4.dynv6.com/api/update?ipv4=auto’&‘zone=YOUR_ZONE’&'token=YOUR_HTTP_TOKEN”
Your zone is found under My Zones.
The token is found by clicking on your login name (upper right of the screen) and clicking KEYS then click DETAILS to copy your HTTP TOKEN.
I recommend you copy and paste the Parameter above as it is critical you only use single quotes around the & symbol.
Test your HTTP string by simple pasting it into your browser and you will get a return message: