Why Shadow Spend Starts Before the PO (and AP Can't Fix It)

Picture an invoice landing in your AP inbox for $18,000. There's no PO attached. Nobody in finance has heard of the vendor. After a few emails you find out the marketing team hired an agency six weeks ago. The work is done, and the agency would like to be paid this month, please.

AP can do a few things here. They can chase an approval, raise a PO after the fact so the invoice matches, code it to the right GL account and pay it on time. What they can't do is go back six weeks and ask whether you needed a new agency at all, or whether you already had one under contract at a better rate.

That decision was made upstream, in a conversation finance was never part of. That's the uncomfortable truth about shadow spend. By the time it shows up in AP, it's already a done deal.

This article explains why shadow spend is an intent-stage problem and why invoice-first tools can only ever tidy up after it. Then we'll look at what spend control looks like when it starts at the moment someone decides to spend.

Where a purchase actually begins

Most finance processes treat the purchase order as the start of a purchase. In practice, it rarely is. A purchase starts with someone deciding they need something, and that decision almost never happens inside a procurement system.

It happens in a Slack thread where a team lead says "let's just get a contractor for this". Or on a call with a supplier who offers a deal if you sign this week, or when someone clicks "start free trial" and puts a card in. We call this moment spend intent, and it's where the real decision gets made: what to buy and who to buy it from.

Everything that happens after that point is mostly paperwork catching up with a decision that's already been made. The PO, the receipt, the invoice and the payment all follow from it.

The numbers show how often that paperwork arrives late. APQC's open benchmark puts the median share of purchase orders created after the supplier invoice arrives at 10%, across 728 organisations. That's one in ten POs written to justify a purchase that already happened. And that only counts the spend that eventually got a PO. Card spend and expensed software never get one at all. Zylo's 2026 SaaS Management Index found expense-based SaaS spend jumped 267% in a single year.

This is the gap between procure-to-pay and Intake-to-Pay. If you want the full comparison, we've covered it in Intake-to-Pay vs Procure-to-Pay.

What AP is built to do, and where it stops

Accounts payable is good at what it was designed for. An invoice comes in, AP checks it against the PO and the goods receipt, routes it for approval if something doesn't match, and pays it on time. Modern AP tools have made that process faster and cheaper. Ardent Partners' AP Metrics that Matter in 2025 found best-in-class teams process an invoice for $2.78 in 3.1 days.

The catch is in the order of events. AP's whole job starts when the invoice arrives. Every control it has, from three-way matching to approval routing, works on a bill for something that's already been bought.

So when shadow spend reaches AP, the options are limited:

Pay it. This is what happens most of the time, because the supplier has delivered and holding payment just damages the relationship.
Chase an approval after the fact. Someone senior signs off on a decision they had no say in. The approval exists on paper, but it doesn't change anything.
Raise a retro PO. The invoice now matches, and the purchase looks compliant in every report. UCSF's supply chain team describes these after-the-fact POs as unauthorised purchases that bypass safeguards like separation of duties.
Dispute it. Rarely worth it once the work is done, and it leaves the employee who made the commitment in an awkward spot.

None of these options give you back the choice you lost upstream. That's why AP teams feel the pain of shadow spend more than anyone else, yet they have the least power to prevent it. Ardent's survey found invoice exceptions are the top AP challenge for 53% of teams, and 41% say approvals take too long. A lot of that friction traces back to purchases that skipped the front of the process.

Four ways spend gets committed before a PO exists

Shadow spend doesn't look the same every time, but it almost always starts in one of these places.

1. A conversation with a supplier

A manager emails a supplier they've used before and asks them to start. Or they agree a statement of work on a call and the paperwork "will follow". In many cases the company is effectively committed the moment the supplier says yes. The PO, if it ever arrives, is a formality.

2. A card and a free trial

Software is the easiest thing in the world to buy without asking. A free trial turns into a paid plan, and the charge lands on a corporate card or an expense report. AI tools have made this explode. MIT's research on the shadow AI economy found 90% of employees regularly use personal AI tools for work, while only 40% of companies have official subscriptions. We go deeper on this in Expensed SaaS: The Software Budget Hiding in Expense Reports.

3. An auto-renewal nobody caught

A contract signed two years ago renews automatically because the notice window passed while everyone was busy. Nobody decided to keep it. It just carried on, sometimes at a higher tier. Usage-based pricing makes this worse: Zylo found 78% of IT leaders were hit with unexpected charges from consumption or AI pricing in the past 12 months.

4. The long tail of small suppliers

One-off purchases from small suppliers rarely feel worth a formal request. Added together, they're a big chunk of spend. The Hackett Group puts tail spend at about 20% of enterprise spend across 80% of suppliers, and only 4% of companies actively manage most of it. We wrote a full guide on tail spend management if you want to dig in.

In every one of these cases, the commitment happens in a channel finance doesn't watch, at a moment finance doesn't know about. By the time there's a document AP can work with, the decision is history.

What it costs to control spend too late

The later you catch a purchase, the less of its cost you can actually change. At intent, you can still pick a different supplier, negotiate the price, use a contract you already have, or decide not to buy at all. At the invoice, all you can really change is how fast you pay.

The money you lose in that gap is mostly invisible, because it shows up as savings you never got. Ardent Partners found every additional dollar brought under procurement's management saves 6% to 12% in the first contract period. Average spend under management is about 71%, which leaves close to 30% of spend where those savings are given up.

Contract compliance tells the same story. Best-in-class procurement teams hit 79.5% contract compliance, while everyone else averages 56.2%. The difference is mostly purchases that were committed before anyone checked for an existing contract.

Then there's the processing cost. PO-less invoices can't match automatically, so they become exceptions. Ardent puts the cost of processing an invoice at $12.88 for an average team, against $2.78 for best-in-class. Retro POs and approval chases both sit in that gap.

We've broken all of this down, with a calculator you can run on your own numbers, in The True Cost of Shadow Spend. For a typical $100M company, the measurable leak comes to around $1.1M a year.

What upstream spend control looks like

If shadow spend starts at intent, spend control has to start there too. That doesn't mean adding more forms. Heavy process is one of the main reasons people go around procurement in the first place. Deloitte's 2025 CPO Survey found 57% of procurement leaders name siloed ways of working as a top barrier to delivering value.

Good upstream spend control comes down to a handful of things:

1.Capture requests where people already are. Requests show up in email, Slack, Teams and calls. If the only official route is a portal nobody remembers, most requests will never reach it. Our guide to procurement intake management covers how to set this up.
2.Check the request before anyone commits. Is there a contract for this already? Do we own something that does the same job? These are quick questions at intent and expensive ones at the invoice.
3.Route approvals by risk as well as amount. A $500 renewal of an approved tool shouldn't wait a week. A new vendor that will handle customer data should go to security, whatever the price. We wrote about why this matters in The $34 Million Lesson.
4.Turn approved intent into a PO automatically. Once a request is approved, the PO should follow without someone retyping it. That way the PO exists before the supplier starts work, and the invoice has something to match against when it lands.
5.Keep watching after the fact. No front door catches everything. Card spend and PO-less invoices still need monitoring, so the gaps get spotted and closed.

When these pieces work together, AP stops being the place where shadow spend gets discovered. Invoices arrive already matched to an approved PO, and exceptions become the rare case they're supposed to be.

How Blackbee AI starts at spend intent

Blackbee AI is an agentic Intake-to-Pay platform. It sits above your ERP and starts where spend actually starts, at the moment someone decides they need something. From there it handles every step in between until clean, structured data lands in your ERP.

The Intake Agent picks up spend intent at its source. That includes emails, Slack, Teams and forms. People ask for what they need the way they already do, and the request gets captured and checked against your policy before anyone commits to a supplier. It also works out whether the request needs a PO and who should approve it.

The Procurement & PO Agent turns approved intent into a PO. It builds the PO from your contract pricing, so the PO exists before the supplier starts work. It tracks delivery and closes the PO when the work is done. Your ERP sees every status change along the way.

Those two agents cover the front of the process, which is where shadow spend begins. The rest of the suite picks up from there. The Contract Intelligence Agent checks requests and invoices against your agreements, the Approval Orchestration Agent routes by risk and policy, the Vendor Relations Agent vets new suppliers before the first PO, and the Spend Intelligence Agent watches for anything that still slips through.

By the time an invoice reaches AP, it has an approved request and a PO behind it. AP goes back to doing what it does best, which is paying the right bills on time.

Of course, all of those steps are within your explicit control. You choose what Blackbee AI handles, and it does only that, and does it well.

Start where the spend starts

Shadow spend will keep turning up in AP for as long as the controls only start at the invoice. Moving the control point upstream, to the moment of intent, is what changes the outcome. It gives finance a say while the decision is still open.

If you'd like to see how Blackbee AI captures intent and turns it into an approved PO before the supplier starts work, book a 30-minute demo. Curious what shadow spend is costing you right now? Try the free Shadow Spend Calculator.