Supplier invoice matching when you do not have an accounts payable team
Supplier invoice matching checks whether the invoice you received matches the purchase order that authorized the spend. Two-way matching handles most of what a small business gets wrong. Three-way matching adds value only once goods receipts are being recorded consistently.
Supplier invoice matching checks two things at minimum: whether the supplier invoice matches the purchase order that authorized the spend - same supplier, same items, same price, same quantity. That two-document comparison is called a two-way match, and for a business of ten people, it is the minimum that works. The fuller version, a three-way match, adds a goods received note to confirm that what was invoiced actually arrived. Most small businesses should start with two-way matching and add the third check only once they are consistently recording deliveries anyway.
What two-way matching actually checks
A purchase order authorizes a purchase before it happens. It names the supplier, the items or services, the agreed quantity, and the agreed price. A supplier invoice requests payment for goods or services already delivered. Two-way matching checks that the two documents agree.
The errors it catches are the ones that cost small businesses money: an invoice at a price that was never agreed, a quantity that differs from what was ordered, a line item that does not appear on the original purchase order, or an invoice from a supplier no one placed an order with. For a business without a dedicated accounts payable function, these are the practical failures to catch - not abstract fraud schemes, but genuine billing errors and supplier mistakes that happen on ordinary transactions.
The purchase order is the anchor. Without one, there is nothing to match against. Businesses that authorize purchases by email approval or verbal agreement cannot run this check at all. The discipline of raising a purchase order before placing an order is what makes matching possible - and it costs less to build than it looks, because the purchase order also becomes the reference point for chasing deliveries, querying suppliers, and reconciling the purchase ledger at month end.
One related problem
Even with a purchase order in place, invoices often arrive with no PO reference, making them harder to match quickly. Asking suppliers to quote your PO number on every invoice - and treating an invoice without one as a query rather than an approval - closes this gap before it becomes a backlog.
Why three-way matching depends on a discipline you may not have yet
Three-way matching adds a goods received note (GRN) to the comparison. A GRN records what arrived, when, in what quantity, and in what condition. With all three documents in place, the check confirms not just that the invoice matches the order, but that the goods were actually delivered before payment is released.
The limitation is what happens when GRNs are missing or inconsistent. For the third check to work, someone must record deliveries at the point of receipt - the date, the supplier, the purchase order reference, the items, and the quantity. In a small business, this step is often skipped, recorded from memory at the end of the week, or not done at all. When goods receipts are incomplete, three-way matching creates a queue of exceptions that stall invoice approval - not because invoices are wrong, but because the receiving records do not exist yet.
That is the reason the thesis holds: three-way matching only pays for itself once the receiving discipline is already in place. If a business holds inventory, manages stock by product, or handles a high volume of physical goods from multiple suppliers, GRNs are probably already being recorded as a stock control measure. In that case, adding the invoice to the comparison is a natural extension. If GRNs are not being recorded at all, the investment required is not the matching logic - it is the operational change needed to start recording deliveries consistently before you can run the check reliably.
Running two-way matching without an AP team
For a business of ten people, the matching process needs to be consistent without being complicated. A few decisions make the difference.
Define when a purchase order is required. Most businesses set a spend threshold - anything above a fixed amount requires a purchase order; recurring authorized expenses like subscriptions and rent sit on an approved standing list. This keeps the process manageable without leaving all spend unchecked.
Give every purchase order a unique reference number and ask suppliers to quote it on their invoices. A missing PO number is a flag to investigate, not a reason to pay quickly and sort it later.
Match invoices before they are approved, not after. It is common in small businesses for an invoice to be approved in a rush and passed to a bookkeeper, with any mismatch surfacing during the next reconciliation. By then the payment may already have left the account.
UK law sets the default payment period at 30 days from invoice receipt for business-to-business transactions where no other date has been agreed - up to 60 days when a payment date is formally agreed between the parties. That timeline matters because a business that catches an incorrect invoice early has time to request a correction before the due date. A business that pays a wrong invoice and then tries to recover the overpayment faces a much harder conversation.
Approving without checking
The most common way two-way matching fails in a small business is not fraud - it is a rushed approval. An invoice that looks right at a glance gets approved before anyone checks the price or quantity against the original purchase order. Building the check into the approval step, rather than treating it as optional, is the only way to make the control reliable.
When to add the third check
The case for adding three-way matching is straightforward: add it when you are already recording what arrives. If goods receipts are being noted against purchase orders as a standard part of receiving - because stock levels need to be updated or partial deliveries need to be tracked - the GRN already exists. Running the invoice against it adds one more comparison to a process that is already happening.
Zigaflow's delivery notes feature records what arrived against each purchase order, creating the formal receiving record that three-way matching requires. For businesses already using purchase orders in Zigaflow, the third document is captured as part of the normal receiving workflow, and supplier invoices can be compared against all three before payment is approved.
The supplier invoice approval problem is often less about the invoice itself and more about the process around it: no purchase order to match against, no clear owner for the approval, and no record of what arrived. Two-way matching resolves the first two. A consistent receiving process resolves the third - and once it does, three-way matching is simply the next step in a process that is already working.
Sources
- Check when large businesses pay their suppliersGOV.UK · accessed 2026-09-12
- Late commercial payments: charging interest and debt recoveryGOV.UK · accessed 2026-09-12
- Three-Way Matching for Small Businesses: The Purchase Order, Receipt, and Invoice Control That Stops Duplicate PaymentsBeancount.io · accessed 2026-09-12
- 2-Way vs 3-Way PO Matching in Accounts Payable: Differences, Benefits and Automation Guide 2026Mindsprint · accessed 2026-09-12
- What is invoice matching? Examples and best practicesRillion · accessed 2026-09-12
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