With Dyn service you can update the A-Record via browser using the following format:
https://{user}:{updater client key}@members.dyndns.org/v3/update?hostname={hostname}&myip={IP Address}
https://help.dyn.com/remote-access-api/perform-update/
However, looks like in the backend they are looking for the User-Agent Field in the HTTP Request, if this field is not present then the record is not updated.
I'd like to perform this update from a network device, not from a browser so it will not send a user-agent. Is this something that can be allowed by Dyn?
I tested other companies and it works OK.