Why POs, receipts, and invoices never agree

If you run AP at a modular factory, you know the feeling. The PO says one thing. The receipt says another. The invoice says a third. Every invoice should pass a three-way match before it gets paid. On a busy week, most of them don’t.

This doesn’t mean your people are careless. A factory buys a lot of material from a lot of vendors. Three different people touch each purchase at three different times.

What a three-way match is

Before you pay a vendor, you check three documents against each other. The purchase order (PO) is what you agreed to buy and at what price. The receipt is what showed up at the dock. The invoice is what the vendor wants you to pay. If the amount and price match on all three, you pay. If they don’t, someone has to find out why.

Most ERPs have a built-in tool that shows you the three-way match. But it’s hard to use it on every bill. Some bills are for materials or inventory, and those need a receipt. Others don’t. It could be a sitework vendor, a lawyer’s bill, or a bill from your accountant (which should always be paid first 😉). I have yet to see an ERP that can sort all the different bills a modular company gets. Most of the time it takes a person’s eyes to catch the mistakes. AI can help a lot here when you set it up with care. But AI that is set up poorly makes mistakes too.

One thing to be clear on: I don’t create POs. PO creation sits fully with your procurement team. I create the purchase invoices (PIs), deal with vendors, review each invoice, and prepare it for payment. Keeping those jobs separate is an important control. The person who orders the material should not be the same person who gets the bill ready to pay.

The mismatches we see most

Missing PO. Sitework runs long, and the porta-potty and fence rental vendors bill for an extra month. Or a freight bill shows up on its own. Nobody made a PO for it.
Partial receipts. Half a shipment of aluminum extrusions shows up Monday. The rest comes Thursday. The vendor bills the full PO on Monday.
Substitutions. The vendor ran out of one window size and sent another. Now the PO, the receipt, and the invoice each show a different part number.
Price changes. The PO has last month’s lumber or steel price. The invoice has this month’s. Which one do you pay?
Receipts entered late, or never. The material is already on the line, but nobody entered the receipt. So the invoice has nothing to match.
Wrong PO on the invoice. Purchasing fixes a PO by making a new one, but nobody tells the vendor. The invoice comes in with the old PO.
PO already used up. The invoice lists a PO, but the whole amount is already used. Nobody approved an overage or a new charge.
Duplicate invoices. The vendor emails the invoice, mails it, then sends it again with a statement. Each copy looks new.

The one I run into most is a bill with no PO. Full-service modular companies have so many vendors and service providers. A new welder might come in for one urgent part of a job, and nobody thinks to make a PO. Two others come up a lot too: a PO that has been over-received, and a receipt, purchase invoice, and PO that don’t quite match. Smaller vendors often make that last one a lot when they send an invoice.

What each one costs if nobody chases it

Every mismatch that sits in a pile turns into one of these problems:

You pay for material you never got. Or you pay the new price when the PO has the old one.
You pay the same invoice twice.
Inventory and job costs are wrong, so the profit on the build is wrong.
Vendors put you on hold or stop giving you terms, because their bills sit unpaid while you sort it out.
Month-end takes longer, because the close has to clean up what AP couldn’t.

Here’s a real one. A company rented most of its install equipment and its factory forklift from one rental company. They fell so far behind on the bill that they got a final notice. It said the rental company would take legal action if they didn’t pay the late bill and all the late fees.

Thankfully, someone read the letter and paid fast, before any legal action was taken. So why was it missed? The person who made the rental POs had left the company, and that job fell through the cracks. The invoices kept coming in. But purchasing was swamped, so no POs got made, and the bills couldn’t go through the payment process.

A simple routine that keeps them small

I check the AP email inbox on a set schedule each week. That might be Monday, Wednesday, and Friday, or Tuesday and Thursday, or just Wednesday. It depends on how many bills you get and what you need.
When a vendor invoice comes in, I enter it as a purchase invoice (PI) right in your ERP. I also attach the vendor’s invoice to the PI.
Some invoices don’t say which PO they go with, or they have one of the problems above. I put those on one list. Each item goes to the right team: purchasing, sitework, logistics, or receiving.
I post the open list where your team already talks (Slack, not a long email chain). I say clearly what help I need from each team to get the invoice ready to pay.
I check the list every time I check the inbox, so it never falls behind. Anything overdue gets an extra flag.

At the start of a new client, I often meet with each team every week or every month. I explain how and why I need their help on certain vendor invoices. This often leads to a better, tighter process for everyone. For example, one client’s Home Depot Pro invoices never had the right PO on them, even though their team had made the PO. A big pile of invoices built up. When I talked with purchasing to help clear it, they told me they had a great relationship with their Home Depot rep. One phone call later, Home Depot Pro was adding the right PO. That gap between purchasing and AP is what I help close.

Where outsourced AP fits

Some factories have an AP clerk or an office manager doing all of this alongside ten other jobs. Our Outsourced AP service takes the matching and chasing off their plate. We work inside your ERP, your AP inbox, and your payment system, alongside your procurement team. Your people keep purchasing, receiving, and approving payments. Every step is supervised by a CPA.

If your open AP list is longer than your paid list, book 15 minutes and bring it.