It very common to do customizations on this indeed. The PO may have an outstanding amount that will never be recieved/invoiced (ex: yearly PO but not everything has been used/consumed), especially for services.We don't want to modify the PO, it must be kept as it but there should be either an additional field or an additional "Status" to flag it as "Closed". And it should also be possible to delete PO which are closed even though they have an outstanding amount.As a consequence of this statuts, the tiles on the different role center should take into account this "Closed" status to show only the volume of unclosed PO. And on the project module, the outstanding amount should ignore closed purchase orders.New receipts/invoices should not be possible if the PO is closed so there should be an action to unclose the PO if needed.