Receive purchase order lines. POST
Book received quantities into stock. Average cost updates and waiting backorders are filled. Returns 409 `APPROVAL_REQUIRED` with an `approvalId` when an approval policy wants a decision first.
Record an invoice payment. POST
Records a manual payment (bank transfer, cash, card, or other) against a sent or overdue invoice. Partial payments keep the invoice open; the payment that settles the balance marks it paid.
