Getting an Agency Invoice Through Client Procurement

Your statement of work is signed, the campaign shipped, and you send the invoice on the first of the month. Three weeks later it is still sitting somewhere between the marketing lead who hired you and an AP inbox you have never emailed. Nobody is being rude. You just walked into a procurement process you were not set up for.

Procurement at a mid-size or enterprise client is a checklist, not a conversation. If the invoice matches the checklist, it pays. If one field is wrong, it gets kicked back, and the clock restarts. Here is how to set up the first invoice with a new client so it clears on the first pass, and how to keep the second, third, and twentieth invoices moving without drama.

Get the procurement requirements before you send anything

Before the first invoice goes out, ask your day-to-day contact four questions in one email. What legal entity should be billed? What billing address belongs on the invoice? Is a purchase order required, and if so, who issues it? Who is the AP contact, and do they use a vendor portal?

That email saves you a month. The marketing director who hired you is probably billed through a parent holding company you have never heard of. The address on their website is the office they work from, not the address AP wants printed on the invoice. And the PO almost certainly has to exist before you invoice, not after. If the client says they need you onboarded in their vendor portal, read what to do when a client wants you in their vendor portal before agreeing to anything that locks you out of your own records.

Build the invoice to match the PO, line for line

AP matches three documents: the PO, the goods receipt (or service confirmation), and your invoice. This is called three-way matching, and it is the single most common reason invoices get rejected. If the PO says Q3 Paid Social Management, 12,000 USD and your invoice says Social campaign work, July, 4,000 USD, the match fails. The amount is fine. The wording is not.

Mirror the PO. Use the same line item description, the same unit, the same currency, the same total. If the PO is for 12,000 USD across three months, decide upfront whether you bill 4,000 USD against it three times or 12,000 USD once, and put the PO number on every invoice that draws against it. If you are unsure what a PO actually is or what format the client's looks like, the guide to purchase orders and the PO number format checker will save you a guessing game.

What AP looks for, field by field, is covered in the AP field checklist. The short version: invoice number, issue date, your legal entity and tax ID, their legal entity and billing address, PO number, line items that match the PO, currency, subtotal, tax, total, payment terms, due date, and bank details. Anything missing is a reason to reject.

Let the client fix their own details without restarting the invoice

Here is where most agency invoicing falls apart. You send a PDF. The client emails back: "Can you change the bill-to entity to our UK subsidiary and add PO 4477123?" You edit the PDF, resend. They reply: "Also the AP contact should be ap-uk@, not ap@." You edit again. By version four nobody knows which PDF is current and the due date is already past.

This is exactly the loop invoicing built for agencies is designed to remove. You send a link, not a PDF. The client opens it and edits the PO number, the billing entity, the billing address, and the AP contact themselves. Those are tracked amendments to the current invoice, not new versions, so the invoice number stays the same. You get notified, you can revert anything that looks wrong, and the bank details and invoice number stay locked. If they need a line item or the payment terms changed, that goes through a change request you approve, which creates a clean V2.

The same flow handles the moment your contact says "actually, can you add a PO number now?" two weeks after you sent the invoice. The walkthrough for adding a PO after sending covers it. No new PDF, no new invoice number, no confusion in their books or yours.

Forward to AP the way AP wants to be forwarded to

Your contact is not the person who pays you. Once the invoice is correct and your contact has approved it internally, it needs to land in the AP inbox or vendor portal with everything attached. The cleanest path is to let the recipient forward the invoice link to AP directly from inside the invoice, so AP sees the same live document, not a forwarded email chain with a stale PDF. The mechanics are in how to forward an invoice to accounts payable.

If the client requires a PDF for their portal upload, download one from the same invoice. The PDF and the link will always agree, because they are generated from the same record. That matters when AP asks six weeks later why the PDF in their system shows a different billing entity than the one in their ERP.

Set payment terms that survive a 30-day approval window

If procurement takes two weeks and AP takes another two, Net 30 from the invoice date means you are already late before anyone has opened the file. Either issue the invoice the day work is completed and accept the timeline, or negotiate terms that start from approval rather than issue. Why Net 30 invoices pay late goes into the failure modes, and the comparison of Net 15, 30, and 60 is useful when a new client pushes back on your standard terms.

For an agency running multiple clients with different procurement quirks, the pattern is the same every time: ask the four questions before you invoice, mirror the PO exactly, let the client edit their own billing fields, forward to AP through the live invoice, and pick terms that account for their approval window. Set that up once per client. Every invoice after the first one clears in a week.

Ready to try this with your next invoice? Create one in a couple of minutes and send the link instead of the PDF.