after you issue a PO, the supplier issues an invoice which has to be recorded as a purchase invoice by you. you pay the supplier based on this purchase invoice and not your PO.
Be aware that the workflow Purchase order - Purchase invoice - Good receipt works throughout Manager.
Which means you can’t make Purchase Invoices directly based on your Goods Receipt, as you know now.
It also means that before you can make a financial report check wether you have booked the corresponding Purchase Invoices for the Goods Receipts. So you should not have open Goods Receipts at closing date. It can cause a false Inventory Cost figure and Inventory on Hand figure.
If you have Purchase Invoices and no corresponding Goods Receipts then there will be no problem with your Inventory Cost and Inventory on Hand figure.