Learn why large clients use Purchase Order numbers, where to put them on your invoice, and why including them is critical for payment.
If you work with large corporations or government entities, you will inevitably deal with a Purchase Order (PO) number. Ignoring it guarantees payment delays.
What is a Purchase Order (PO)?
A PO is a legally binding document issued by the *buyer* to the *seller*. It authorizes a purchase and defines the terms and conditions. It is essentially the client's internal budget approval.
PO vs. Invoice
| Document | Creator | Timing | Purpose |
|---|---|---|---|
| Purchase Order | Buyer (Client) | Before the work | Authorize the purchase/budget |
| Invoice | Seller (You) | After the work | Request the payment |
Why the PO Number is Critical
A client’s Accounts Payable department will often **not process your invoice** without a valid, matching PO number. It's how they link your request to their internal authorization.
Where to Put the PO Number
It should be clearly visible near the top of your invoice, close to the Invoice Number and Due Date.
Invoice ASAP includes a dedicated field for PO numbers, ensuring you never forget to include this crucial detail when billing larger clients.