When to use a PO — and how to handle “missing PO” replies

“Missing PO” is one of the most common reasons a valid invoice gets stuck.

It also creates a specific kind of delay. Not drama. Just admin gravity.

The fix is not more reminders. The fix is a clean workflow.

This post covers two things:

• When a PO helps (and when it slows you down).
• How to handle “missing PO” replies so the invoice moves into approval and payment.

Why “missing PO” causes avoidable payment delays

Most larger buyers run controls in their procure-to-pay process. They match invoices to purchase orders (and sometimes to a receipt) before they approve payment. GOV.UK guidance calls this out as a key control: two-way match (PO + invoice) or three-way match (add goods receipt note). GOV.UK

So when a customer says “missing PO”, they usually mean one of these:

• Their system will reject the invoice without a PO number.
• Someone cannot approve spend without a PO.
• The invoice needs a portal submission linked to a PO.

If you keep chasing “please pay”, you create noise. You do not remove the blocker.

When you should use a PO (and when you shouldn’t)

Use a PO when approval and matching matter

A PO helps when the buyer needs an internal approval trail. Common cases:

• Mid-market and enterprise accounts with strict procurement.
• Public sector accounts (often “No PO, no pay”). GOV.UK
• New suppliers (they want formal controls early).
• One-off or high-value purchases.
• Anything that needs invoice matching and audit trails.

A PO can also reduce disputes because it anchors “what was ordered” and “what was approved” inside the buyer’s process.

Skip the PO for repeatable, low-risk spend

A PO can also be overkill. Many organisations treat certain spend as “non-PO” and match invoices to contract terms instead (utilities, rent, recurring services). GOV.UK describes non-PO purchases as cases where teams match contract terms against invoices received. GOV.UK

In SaaS, you often see this pattern:

• Low-to-mid value recurring subscriptions: contract + invoice works fine.
• Enterprise licence expansions and one-off professional services: PO becomes more common.

A simple decision checklist

Use a PO when you answer “yes” to any of these:

• Does the buyer require a PO for this vendor or spend category?
• Will AP reject invoices without a PO number?
• Is the invoice value above their approval threshold?
• Is this a new supplier or a new service line?
• Will the work be delivered via a portal workflow tied to a PO?

If you answer “no” to all, pushing for a PO may slow things down.

What buyers do with a PO (so you can work with it)

In many finance teams, the PO is not just a reference. It is the key that unlocks payment.

Their system tries to match:

• PO details (what was approved), and
• Invoice details (what you billed).

Sometimes they also match a receipt (proof of delivery). GOV.UK

That means small mismatches can block payment:

• PO number missing or wrong.
• Legal entity mismatch.
• Line item descriptions too vague to match.
• Amount exceeds PO remaining balance.
• Service period not obvious.

Your goal is to make matching easy.

The “missing PO” workflow we use (reply → tag → unblock → paid)

We keep this boring and repeatable.

Step 1: Tag the reply and stop random chasing

As soon as the reply lands:

• Tag it: Missing PO.
• Pause the standard reminder cadence for that invoice.
• Set a short follow-up date (48–72 hours) while you unblock.

This matters because your next email should not be “Please pay”. It should be “What do you need to process this?”

Step 2: Ask the right 5 questions

You can resolve most missing PO cases with five questions:

1. Who raises the PO (name + role)?
2. What is the PO creation timeline (same day / this week / next run)?
3. Do you need the PO number on the invoice, or is portal submission required too?
4. Any specific invoice requirements (vendor name, address, tax IDs, line item format, service period)?
5. Who should we copy for approval (buyer, AP, procurement)?

This turns “missing PO” from a vague excuse into a tracked workflow.

Step 3: Push the blocker to the right owner (same day)

This is where teams lose weeks.

A PO often sits with:

• the internal buyer,
• Sales Ops / Deal Desk, or
• Customer Success (if they own expansions).

So we push a clear blocker message into the internal channel:

• Blocker: Customer requires PO before payment.
• Invoice: #10482 (£6,400), due 18 Nov.
• Ask: Please confirm the buyer contact and who will raise the PO.
• Deadline: EOD tomorrow.
• Next step: We will re-issue invoice with PO and submit via portal if required.

Short. Owned. Timebound.

Step 4: Re-issue the invoice cleanly (Stripe included)

Once you have the PO number, do not bury it in an email thread.

Put it on the invoice in a consistent place.

If you use Stripe Invoicing, you can add PO numbers as custom fields on the invoice (and even inherit those fields from the customer settings while the invoice is still in draft). docs.stripe.com

Practical rule:

• If the buyer uses POs, create a standard invoice field called “PO number”.
• Keep the value exact (no extra words, no punctuation guesswork).
• Re-send the updated invoice and confirm the next approval step.

Table: Missing PO triage playbook (owner + SLA + next step)

What you do	Why it matters	Owner	SLA	Output
Tag reply as “Missing PO”	Stops useless chasing	AR owner	Same day	Correct workflow starts
Ask 5 PO questions	Gets the real blocker	AR owner	Same day	PO owner + timeline
Post blocker internally	Creates accountability	Finance/RevOps + account owner	Same day	Named owner + deadline
Update invoice with PO	Prevents rejection	AR owner	24–48 hrs after PO	Re-issued invoice
Confirm submission route	Many buyers need portal steps	AR owner / Ops	24–48 hrs	“Approved for payment” path
Follow up on PO date	Keeps it moving	AR owner	On agreed date	Next-step confirmation

Email snippet you can copy (customer-friendly)

Subject: PO details needed to process invoice 10482

Hi Jamie,
Thanks for the note. Happy to align to your PO process so AP can approve invoice 10482.

Could you confirm:

1. Who will raise the PO (name/team)?
2. When we should expect the PO number?
3. Do you need the PO number on the invoice only, or also a portal submission?

Once we have the PO, we’ll update and resend the invoice the same day.

Thanks,
BSB AR Team (on behalf of Your Company)

It is calm. It is specific. It gives them an easy next step.

Common pitfalls (and fixes)

• Pitfall: treating missing PO like a late payer.
  Fix: treat it like an ops workflow with owners and dates.
• Pitfall: waiting for the customer to “figure it out”.
  Fix: ask who raises the PO and what they need from you.
• Pitfall: patching by email only.
  Fix: put the PO number on the invoice itself. Use a consistent field. docs.stripe.com
• Pitfall: no internal owner.
  Fix: push the blocker into the channel where work happens.

What to review weekly (founder view)

Add these to your weekly receivables report:

• Total value tagged “Missing PO”.
• Oldest missing PO item (and who owns it internally).
• Average time from “missing PO reply” to “invoice updated with PO”.
• Any accounts with repeat PO friction (candidates for portals/onboarding support).

This keeps “admin delays” visible, not mysterious.

If “missing PO” and portal steps keep slowing cash, we can run the workflow for you.

We plug into your tools, read every reply, tag the reason, and push blockers to your team so cash keeps moving. If a buyer needs a PO or portal step, we see it early and handle the workflow.

Explore “Managed AR Ops” and “AR + Portals & Onboarding” on services. If you want to talk through your setup, Get in touch via contact.

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Compliance & clarity: This post shares general operational guidance. It is not legal, tax, or accounting advice. Examples are illustrative and do not include private client data.