List of items to update. Example: [{ identifiers: { identifier: 'abc' }, item_id: 123, item_size: 'M', quantity: 1 }]

Operation on items (update_item/remove_item). Example: update_item

Free gift items to update. Example: [{ promotion_id: 'PROMO1', item_id: 'SKU1', item_size: 'L' }]

Operation for free gift items (add/remove). Example: add