The Order Document Preview API is required to be called before confirming an Order. This API is meant to return a unique order id for documents selected in the preview.
Order Preview accepts documents of a single case. If you want to preview documents from different cases, then you need to make one request per case.
Note: A single Order Preview is limited to 20 documents per API call. This API accepts document_ids (comma separated) and case_id within POST method.