After frustrating back and forth about private APIs (coudfront is prvate apparently). I got the simlpe answer whihc could have been given immediatly - YOU CAN NOT DO THIS.
From support "Additionally, Zephyr Scale Cloud currently does not offer a public endpoint to handle attachments. Images can only be added or downloaded through the UI. Unfortunately, it is not possible to add or download images via the REST API at this time. It is expected to be available within the next few quarters."
So the API is incomplete (to say the least).