The Zotero collection should be describe as the ID of the collection (e.g. fetched with the additions you did for Zutilo).
Items should be specified as with reference to their LocInArchive. The LocInArchive is something like A;B;C. The command
addto_collection_byLocationInArchive collectionID B
would add the item with LocInArchive A;B;C to collection wtih collectionID.