The purchase order number set by the buyer.

ordrsp_Examples
 <documentReference documentType="BuyerOrder" id="555666" date="2020-08-25" lineNo="2" parentLineNo="1">
ordrsp_XPATH

/b24Message/orderResponse/item/documentReference[@documentType="BuyerOrder"]/@id

ordrsp_Type
Text
ordrsp_Sort
11100
Subscribe to Buyer order number id (Item/Line)