The following F.A.Q. intends to clarify what is and is not possible to do with related documents.
Q. Can I send a mapping.json file in a ZIP archive without any file?
In the case where you just want to detach an already attached document, you can send the mapping.json file without the lines concerning the specific document in an empty archive. The archive must then be uploaded as FULL.
Q. I want to send a new publication (book/DITA map) with a related document, can I do it in one upload?
You need to upload your structured content first, then retrieve the mapping.json.
Q. Do I have to perform the action to get the mapping.json file every time I want to upload new attached content?
While it is not necessary to get the mapping.json file every time you wish to update your attached documents, it is nonetheless STRONGLY recommended in order to always work with the latest available version of the mapping.json file.