The PO lifecycle
- Buyer creates the PO with numbered lines and prices
- Supplier accepts (silently by shipping, or explicitly)
- Goods or work are delivered against the PO
- Seller invoices referencing the PO number
- Buyer's finance matches PO + delivery + invoice, then pays
Why the PO number matters on invoices
Corporate buyers pay through three-way matching: the invoice is checked against the PO and the delivery record. No PO reference means a manual investigation — the single most common cause of invoices sitting unpaid for weeks. Ask for the PO before starting work and print it on the invoice.
PO vs contract vs invoice
The PO is the offer and, once accepted, the contract for this transaction. Framework agreements sit above it; invoices sit below it. For small purchases the PO alone is the whole contract — which is why its wording and prices deserve the same care as a contract.
Frequently Asked Questions
Who keeps the original PO?
The buyer creates and owns it; the supplier gets a copy to invoice against. Both archive it — auditors check PO-to-invoice completeness.
Can a PO be changed after issuing?
Yes, by issuing a revised PO with a new version or amendment number — never by editing the original. The seller invoices against the latest accepted version.
Do freelancers need to issue POs?
Freelancers are usually the supplier — they receive POs. If a corporate client cannot give you a PO number, ask for the engagement reference in writing instead; it serves the same matching purpose.