Using HTTP POST to create a new post in All Company function as expected, except the image (attached_objects) is not added to the new post.
The image is already uploaded to the corresponding All Company SharePoint site. Selecting Yammer > Settings > Export Data creates a CSV file with two ids for the image file: id and file_id. I've tried both ids in the HTTP POST below (e.g 1164502745088), but no image is added to the Yammer post.
"title": "Kunngjøring med bilde test 6.7",
"body": "Dette er linje 1<br>linje 2<br><a href="https://gorovian.000webhostapp.com/?exam=http://vg.no'>Julekalender</a>.",