Hello,

Unfortunately, I don't believe that we have support for setting values for "Attachment" fields through these APIs. Giving a path to a file that's under the file/pipeline root for a given folder should work for "File Link" fields, but lists don't currently allow for that field type. For reference, File Links are just stored as a path (a pointer to a file), while Attachments store the binary content of the file itself.

Thanks,
Josh