Purchase Order (PO Number)
A purchase order is a business’s own reference number for work it has already approved internally, issued before you invoice. Put it on the invoice exactly as given, or their accounts system may not match your payment.
What it means
A purchase order, or PO, is the business’s own internal control — proof to their accounts department that someone with the authority to spend actually approved this job before it happened. They generate the number, not you; your job is to put it on the invoice exactly as given, in whatever field or reference line their process expects.
It matters because a company invoice missing the PO number their system is looking for often just sits — not refused, just unmatched, until someone chases it and finds the gap. Ask for it at the same time you confirm the accounts contact and the payment terms, before the job starts, not when it comes time to invoice.
A commercial client gives you a purchase order number, “PO-4471,” when they book the job. You put it on the invoice exactly as given, and their accounts team matches it against their own approval record and pays without a query.
Starting the job without asking whether a purchase order applies, then having the invoice bounce back weeks later asking for one — a five-second question upfront that turns into a real delay in getting paid.
See also
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