How do I get a purchase order number from a client before invoicing?
How to get a PO number from a client before you send an invoice
Short answer
Ask for the PO number before you begin work, not after you invoice. Include it as a required field in your proposal or service agreement: 'Please provide a purchase order number so we can reference it on your invoice.' Most large companies issue POs automatically once a purchase is approved — if they haven't sent one, escalate to their procurement or accounts payable team, not your day-to-day contact.
A purchase order is a formal document the client's finance or procurement team issues to authorize a purchase. Without a PO number on your invoice, accounts payable departments at larger companies often can't process payment — it's a system control, not a delay tactic. The fix is to build PO collection into your onboarding, not your invoicing.
When you're scoping a project with a new corporate client, ask directly: 'Will your company require a purchase order number for invoicing? If so, can you send that over once the project is approved?' This surfaces the requirement before any work starts and signals that you're experienced with corporate processes. If they say yes, don't start work until you have the PO number in writing.
If you've already delivered work and the client now says they can't pay without a PO, that's a problem they created — but you'll still need to solve it. Ask your contact to expedite a retroactive PO. Most finance teams can issue one if the business need is documented. In parallel, get confirmation in writing that the invoice is approved pending PO issuance, with a specific date. This protects you legally if they later deny the obligation.
Some clients use the PO system as an informal delay mechanism — they're slow to issue POs, which means your 30-day terms effectively become 60. Address this in your contract: 'Payment terms run from invoice date, regardless of PO issuance date.' This is enforceable and shifts the incentive back to the client to move their procurement process quickly.
For recurring clients, set up a PO number lookup as part of your standard annual or project kickoff. Many companies issue blanket or standing purchase orders for vendors they use regularly. One PO can cover an entire year of work, which eliminates the per-project procurement delay entirely. Syntharra's invoicing integrations with QuickBooks, Xero, and FreshBooks support PO number fields natively — once the number is on the invoice, the follow-up process runs as normal.