Non-PO invoices: how AI agents validate them without a match

Non-PO invoices are supplier invoices that arrive with no purchase order behind them. Nothing was ordered through procurement, so the accounts payable system holds no prior record of what was agreed, at what price, or on whose authority, and the automated match has nothing to compare the invoice against. Validation has to be reconstructed from other records: contracts, approval policies, and the supplier's own billing history.

This wiki defines procure-to-pay terms the way an AI agent working the process meets them. Agents read the contracts, run the matches, and clear the exceptions; the people they work alongside keep the calls that need judgment. A standard glossary tells you a non-PO invoice lacks an order and stops. This page covers what an agent reaches for in place of one.

A non-PO invoice arrives with its proof structure missing

A purchase order does more than authorize a purchase. It records the agreed price and quantity, names the approver, carries the accounting treatment, and gives three-way matching – the line-by-line comparison of invoice, purchase order, and goods receipt – its reference points. A PO-backed invoice that agrees with those references posts without anyone touching it. A non-PO invoice has none of that, and for most services there is no goods receipt either – the record confirming what physically arrived – because nothing physical showed up to be counted. Every fact the match would have verified still has to be established before payment, and no single document states them.

Most non-PO spend resists being ordered in advance: outside counsel billing by the hour, consultants invoicing against milestones, utilities metering usage after the fact, rent and facilities charges set by lease. In many AP operations these invoices flow straight into the invoice exceptions queue, alongside the failure modes the types of invoice exceptions page catalogs, and they sit longer than matched invoices because clearing one means finding whoever knows the work happened.

Four kinds of records substitute for the purchase order

The evidence needed to validate a non-PO invoice usually exists, spread across systems that never talk to the matching engine. Four kinds of records do most of the work:

1. Contracts and statements of work. For legal, consulting, and agency spend, the engagement letter or statement of work – the document that fixes scope, rates, and caps for a project – says everything a PO would have said, in prose instead of fields. It typically lives in a contract repository or a shared drive, away from the ERP.
2. Recurring service agreements. Utilities, rent, waste, and facilities contracts define a cadence and an expected range. An electricity invoice for a site that has billed between $11,000 and $14,000 monthly for two years validates largely on pattern; the agreement supplies the account number and the terms.
3. Approval chains and delegation-of-authority policies. A delegation-of-authority policy, or DOA, states who may commit the company to spend, by category and up to what amount. If the requester's confirmation and the approver's signoff fit the DOA, authorization is established even though no PO recorded it.
4. Historical spend for the supplier and cost center. Prior invoices from the same supplier to the same cost center show what normal looks like: typical amounts, typical coding, the approver who has always signed. Deviation from that baseline is the strongest signal that an invoice deserves a closer look.

An analyst validating a non-PO invoice by hand works through the same four sources, one login at a time; an agent consults them in parallel and writes down what it found.

How does an agent validate a non-PO invoice?

Take one invoice end to end: a bill for $28,650 from the outside firm handling a patent dispute, referencing matter 2024-117 – the ID legal departments use to track a case – with 18 partner hours and 30 associate hours itemized. No PO exists and none ever will, because legal spend at most companies runs on engagement letters. An agent picks the invoice up and works the chain:

1. Find the governing document. The contract repository holds an engagement letter for matter 2024-117 with a rate card: partners at $825 per hour, associates at $460.
2. Recompute the invoice. 18 hours at $825 is $14,850; 30 hours at $460 is $13,800; together $28,650, matching the invoice to the dollar. Every rate conforms to the card, and no unapproved timekeeper appears on the bill.
3. Check the cap. The engagement letter caps the matter at $150,000. Prior invoices total $87,200, so this bill takes the matter to $115,850, comfortably inside.
4. Check authorization. The general counsel approved the previous four invoices on this matter, and the DOA authorizes the GC for legal spend to $250,000 per matter.
5. Confirm and post. The agent routes a one-line confirmation to the GC's delegate, attaches the workup – rate check, cap arithmetic, approval precedent – and posts the invoice with the evidence on file.

The manual version of that investigation is a week of queue time: AP emails legal operations, legal operations digs out the engagement letter, someone rebuilds the math in a spreadsheet. The agent's version differs in elapsed time and audit-trail completeness, and in nothing else an auditor would care about.

Non-PO invoices arrive with the coding blank

A PO-backed invoice inherits its general ledger coding – the account, cost center, and internal order the expense books to – from the purchase order, where a buyer settled it at ordering time. A non-PO invoice arrives with that field empty, and someone has to fill it before posting. In many AP teams that someone is a requester who guesses, which is how consulting fees end up booked as office supplies and why coding and approval exceptions form their own category of rework.

An agent proposes coding from precedent. The past 24 invoices from this waste-management supplier for this site booked to account 6240, cost center 4410; the service agreement confirms the category; the proposal goes on the invoice with the history that justifies it. Where an amount spans departments – a consulting engagement split between finance and IT – the agent drafts the allocation and asks the budget owner to confirm it. Coding quality compounds: every invoice coded consistently makes the next one's precedent stronger, and makes the category spend reports procurement runs worth reading.

A first-time supplier with no contract is a judgment call

Reconstruction works when there is something to reconstruct from. An invoice from a supplier with no contract on file, no billing history, and no approval trail gives the agent nothing to check against, and the honest output is an escalation. The same holds for an invoice citing an agreement nobody can locate, a recurring charge that jumps 60% with no rate change on record, or a requester confirming spend beyond their DOA authority. These cases land with a person, with the searching already done, so the review starts at the decision.

The escalation rate falls as the records improve. Every contract added to the repository, every engagement letter with a real rate card, every DOA kept current converts a future judgment call into a future reconstruction. Companies also push spend onto purchase orders where they can, using blanket orders for recurring services. What remains is spend that genuinely cannot be ordered in advance, which is why non-PO invoices persist at even well-run AP operations and why the validation work is worth automating rather than waiting out.

Fragment builds AI agents that handle non-PO invoices exactly this way – reading engagement letters, service agreements, DOA policies, and supplier history inside a company's existing SAP or Ariba environment, posting what proves out and escalating the first-time supplier with the workup attached, with no rip and replace. See the workflows in detail or request a demo.