Modern purchase order system software will allow for workflows to be created to suit individual businesses. Whether based on role or monetary value, custom workflows for purchase orders, invoices and credit notes can be set up to ensure all the correct stages are in place for each document type.
On purchase orders, approvers at all levels have the ability to reject a PO back to the raiser, with auditable comments, that the purchase order can then act on, comment and re send for approval (or cancel); in this way a conversation re PO’s can be had internally until the purchase is fully approved, before being sent by email to the supplier.