How to get a PO number on your Xero invoice before it's due

Summary

• Large companies won’t pay an invoice they can’t match to a purchase order. With no PO number, or the wrong one, the invoice gets parked and misses the payment run.
• The PO usually comes from a different department to the one that pays. Your day-to-day contact or their buyer raises it and accounts payable settles the invoice.
• Xero has no dedicated PO field on sales invoices. The PO goes in the Reference field.
• Using Trove, you can get a PO from the right person before the invoice falls due and automatically attach it to the invoice reference field.
• Trove does this using your draft invoices in Xero and sending every email from your own email account.

Why big customers won’t pay without a PO

When you invoice a small business, the person who receives the invoice usually pays it. Large companies split that job. One person commits the company to a cost by raising a purchase order against an approved budget. Someone else, in accounts payable, releases the cash.

The PO number connects the two. When your invoice arrives, accounts payable matches it against the PO and often against a goods-received or service-received note too. This is called a two-way or three-way match.

Only once the invoice and the PO line up does the invoice go onto a payment run.

What happens to an invoice with no PO

It gets set aside. Most AP systems have a status for this: parked, on hold or blocked. Three things then keep it stuck.

• It’s invisible. Many AP systems don’t proactively tell the supplier an invoice is on hold.
• It’s nobody’s job to fix. The AP clerk can’t approve it without a PO and finding one for you usually isn’t their job.
• It misses run after run. Payment runs only pick up matched invoices. A parked invoice gets skipped every cycle until the PO appears, so 30-day terms drift to 45 days, then 60.

Chasing it like an ordinary overdue invoice makes things worse. A firm reminder to accounts payable lands with people who were never the blocker. The person who can supply the PO sits in a different team.

Start the process of getting a PO early

A PO is rarely one email away. It usually crosses two or three people:

1. Your contact realises a PO is needed and asks their buyer to raise one.
2. The buyer raises it in the company’s procurement system, which may need its own sign-off.
3. The PO number comes back to you, and you add it to the invoice.
4. You send the invoice, PO included, to accounts payable.

Each step adds a few days. That’s why the request has to go out well before the invoice is due.

Furthermore, large companies pay on runs, sometimes fortnightly or monthly. To make a run, your invoice has to be matched a few days before the run closes. One missed run can turn 30-day terms into 45 or 60 days.

Where to put a PO number on a Xero invoice

Xero doesn’t have a purchase order field on sales invoices. Xero users have been asking for one since 2014. The request on Xero’s product ideas board has 218 votes, and in July 2026 Xero said its product teams were interested in exploring it, without committing to anything.

Until that changes, the best place for a PO number is the Reference field. It sits in the invoice header next to the invoice number and dates, and it shows on the invoice your customer receives. It’s also where Trove writes the PO when it collects one for you.

When you add it, make sure to copy the PO exactly. Include any prefix, hyphens and leading zeros. AP systems match on the exact string, and a spreadsheet that strips a leading zero is enough to get an invoice parked.

If you already use the Reference field for your own job or project numbers, you have a clash, because Xero only gives you one. Move your internal reference into the line description or a tracking category, and keep Reference for the customer’s PO.

Three things that get a PO on your Xero invoice on time

1. A request for the PO. A short, friendly note does it: here’s the invoice, please confirm the PO so we can get it onto your next payment run.
2. Sent to the right person. The person who raises POs is often different from the person who pays. Asking accounts payable for a PO they don’t have adds a round trip.
3. At the right time. Ask about 10 days before the invoice is due. That leaves time for the request to cross two or three people and still make the run.

70% of the businesses with the highest collection rates on Trove use pre-due-date reminders. For customers where a PO gates the payment, that head start is the difference between getting paid on terms and waiting for the run after next. Here’s how to set up a reminder before the due date in Xero.

How Trove gets the PO onto the invoice in Xero

Xero can send a reminder before the due date, but it can’t send it to a different person from your overdue chasers and it doesn’t chase drafts.

Trove can do both these things. Here’s how the process works in Trove for a new customer where Trove has no context:

1. 10 days before the due date, Trove sends a pre-reminder from your inbox with the draft invoice to the customer’s accounts payable team. (10 is the default - you can adjust this)
2. If there’s no PO, accounts payable usually replies asking for one.
3. Trove emails the person at the customer who holds the PO number. That’s often your day-to-day contact or their buyer, rather than anyone in accounts payable. You can set this contact up in Trove in advance, or Trove picks them up from accounts payable’s reply.
4. They reply with the PO number.
5. Trove writes the PO into the Reference field on the draft invoice in Xero.
6. Trove approves the invoice in Xero, marks it as sent and emails it, PO included, to accounts payable.
7. After the first time, it makes the PO contact the first step in that customer’s workflow, so the next request for a PO goes straight to the right person.

Every one of these emails goes from your own email account, not from Trove. To the customer, it’s an ordinary conversation with you, and their replies land in your inbox.

Why an invoice with a PO can still get stuck

A PO number gets you past the first check. These catch invoices after that:

• The PO has run out. Many POs are capped at a value. Once earlier invoices have used it up, the next one fails the match.
• The PO is closed. Some companies close POs at the end of their financial year and issue new ones.
• The lines don’t match. If the price, quantity or description on your invoice differs from the PO, the match fails.
• Nobody has booked the receipt. In a three-way match, someone at the customer has to confirm the goods or service arrived. Until they do, the invoice waits.
• It’s addressed to the wrong company. Groups often have several legal entities. The invoice needs to name the one that raised the PO.
• It broke the inbox rules. Big AP teams scan invoices automatically and set rules for how they arrive. One company’s published payment practices report tells suppliers to send one invoice per PDF to an unmonitored invoice inbox, and to send queries to a separate address.

The fix for most of these is the same as for a missing PO: ask early. When you ask for the PO, ask the customer to confirm which legal entity to bill and that there’s enough left on the PO to cover the invoice. If they also make you submit through a supplier portal, here’s what’s involved in invoice uploads to Coupa and SAP Ariba.

Frequently asked questions

Where does the PO number go on a Xero invoice? In the Reference field. Xero has no dedicated purchase order field on sales invoices, so Reference is the standard place, and it shows in the header of the invoice your customer receives. Where to put a PO number on a Xero invoice covers what to do if you already use Reference for something else.

Can I add a PO number after the invoice has been sent? Yes, as long as no payment has been applied. Edit the invoice in Xero, add the PO to the Reference field and send it again. Trove can do this for you when the PO arrives. Our guide to Xero invoice statuses covers what you can change at each stage.

What does “no PO, no pay” mean? It’s a policy, common at large companies and public bodies, that accounts payable won’t pay any invoice without a valid purchase order number. The invoice usually isn’t rejected outright. It’s parked until someone supplies the PO, and it misses every payment run until then.

How far before the due date should I ask for a PO? About 10 days. That gives the customer time to raise or find the PO and still get your invoice onto a payment run before it falls due.