What is a purchase order number, and should your checkout ask for one?

If you’ve ever had an invoice come back with “please reissue with our PO number”, this is why. For the buyer’s company, the PO number is the thread that ties your invoice to a purchase someone was allowed to make.

How a purchase order works on the buyer’s side

1. Someone at the company needs something, say six monitors.
2. They raise a purchase order in their own system, with the items and the expected cost.
3. A manager or the purchasing team approves it, and it gets a number.
4. The buyer orders from you and gives you that number.
5. Your invoice arrives. Their accounts team checks it against the PO, and often against the delivery note too, before paying. This is often called three-way matching.

If the PO number is missing, the invoice usually goes back to the person who ordered so they can find it. That’s where payment delays come from.

Do you need to ask for one?

Ask for it if:

• customers pay you by invoice or on terms such as Net 30;
• you sell to larger companies, schools, hospitals or public bodies, which often use POs for everything.

You can probably skip it if everyone pays by card at checkout. Payment has already happened, so there’s nothing to match. Some customers will still want the number on their receipt, which the order notes box covers.

Three ways to collect it in WooCommerce

1. The order notes box

WooCommerce’s checkout already lets customers add a note to their order. Telling buyers to put their PO number there needs no setup at all.

The downside is that it’s free text. It’s easy to forget, it can contain anything, and it doesn’t stand out on the order or the invoice.

2. A checkout field plugin

A checkout field plugin adds a proper “PO number” field. Depending on the plugin, you can make it required, show it only for certain payment methods, and include it in order emails.

3. A bit of code

WooCommerce has a developer API for adding fields to the block checkout, and the classic checkout’s fields can be changed with filters. A developer can add a PO field in an hour or two and store it on the order.

Tips whichever way you choose

• Label it plainly, for example “PO number (if your company uses one)”.
• Keep it optional unless every customer uses POs. A required field that some customers can’t fill in will stop them ordering.
• Show it on the order confirmation email, so the buyer can check it.

Get it onto the invoice

The PO number only helps if it’s on the invoice the accounts team receives. WooCommerce doesn’t create PDF invoices by itself, so this depends on your invoice plugin or accounting software. Check that it can include custom order fields, and that your PO field is one of them.

POs and approvals

A purchase order is the buyer’s approval process, happening outside your store. Some companies would rather do that approval in the store: the person ordering places the order, and their manager approves it there before it’s paid. If your customers ask for that, see manager approval for B2B orders.