Every purchase order carries a payment status that is separate from ordering and receiving, so you can see what you still owe your suppliers straight from the Purchase orders list.
Mark an order paid
Every PO carries a payment status, separate from its ordering lifecycle - mark it paid from More actions on the PO, or in bulk from the list. Past the Payment due date, unpaid POs show an Overdue badge, and the list's filter dropdown covers both money and delivery: Unpaid, Partially paid, Paid, Payment overdue, and Late delivery (open orders past their expected date - the same orders the "N late" badge above the list counts).
Record part payments
When a supplier invoices an order in pieces, record each payment as it happens: the Payments card on the PO takes an amount (pre-filled to the outstanding balance), a date, an optional method, and a reference like a check number. The order shows Partially paid until the payments reach the total, the card keeps a running balance against the order total, and deleting a payment row undoes it. Once payments are recorded, Mark as paid records the remaining balance as a payment - and the order can only go back to unpaid by removing its payments, so recorded history is never silently erased.
This is bookkeeping inside Stockroom only - it is never pushed to QuickBooks, where bill payment lives.
Good to know
Payment due fills itself in - when a purchase order is marked ordered without a due date, Stockroom derives one from the supplier's payment terms (Net 30 dates it 30 days out; "due on receipt" dates it same day). It's a prefill, not a lock - edit it any time.
To correct the date an order was paid, open it and choose More actions then Edit paid date - a record correction that changes nothing else.