# How Do Purchase Orders Work? The PO Process Step by Step

> How purchase orders work, from the internal request to the vendor's invoice and payment: the seven steps, what a PO includes and where AI helps.

Source: https://learn.ynteractive.com/content/blog/how-do-purchase-orders-work · Updated 2026-10-21 · Free from Stepthrough (https://learn.ynteractive.com)

Quick answer

A [purchase order](https://learn.ynteractive.com/content/glossary/purchase-order) works as an agreement before money moves: an employee requests a purchase, a manager approves it, the buyer sends the vendor a PO with items, prices and terms, the vendor delivers, and [accounts payable](https://learn.ynteractive.com/content/glossary/accounts-payable) pays only when the [invoice](https://learn.ynteractive.com/content/glossary/invoice) matches the PO. The free [invoice approval lesson](https://learn.ynteractive.com/content/invoice-inbox-to-google-sheets-approval-n8n) automates the matching end.

Last updated October 21, 2026

[Take the free module →](https://learn.ynteractive.com/courses/ai-for-accounting-firms/13)Module 13 of the free [AI for Accounting & Bookkeeping Firms](https://learn.ynteractive.com/courses/ai-for-accounting-firms) course, about 14 minutes. No account needed.

By [Robert Breen](https://learn.ynteractive.com/content/about) · Published October 21, 2026 · Updated October 21, 2026 · 5 min read

Finance · Accounts Payable · n8n

This guide walks through each step in order, shows what a PO should include, and explains where an AI workflow takes over the typing without taking over the decisions. It is for office managers, bookkeepers and anyone who has been told "we need a PO number first."

## What are the steps in the purchase order process?

Most businesses follow the same seven steps, even if a small office does three of them in one email. The order matters because each step creates the record the next one checks.

1. **Request.** An employee asks to buy something, often on a [purchase requisition](https://learn.ynteractive.com/content/glossary/purchase-requisition) form: what, how many, why and roughly what it costs.
2. **Approve.** A manager or budget owner says yes. Many companies set an [approval threshold](https://learn.ynteractive.com/content/glossary/approval-threshold), such as anything over $1,000 needs the owner.
3. **Create the PO.** Purchasing turns the approved request into a [purchase order](https://learn.ynteractive.com/content/glossary/purchase-order) with its own [PO number](https://learn.ynteractive.com/content/glossary/purchase-order-number) and sends it to the vendor.
4. **Vendor accepts.** The vendor confirms the order, prices and dates. From here the PO is the agreed deal.
5. **Receive.** The goods arrive or the service is done, and someone records what actually came in, sometimes on a [goods receipt](https://learn.ynteractive.com/content/glossary/goods-receipt).
6. **Invoice.** The vendor bills you and quotes your PO number on the [invoice](https://learn.ynteractive.com/content/glossary/invoice).
7. **Match and pay.** Accounts payable compares the invoice with the PO (a [two-way match](https://learn.ynteractive.com/content/glossary/two-way-match)) or with the PO and the receipt (a [three-way match](https://learn.ynteractive.com/content/glossary/three-way-match)), then pays on the agreed [payment terms](https://learn.ynteractive.com/content/glossary/payment-terms).

The full cycle from request to payment has a name, [procure-to-pay](https://learn.ynteractive.com/content/glossary/procure-to-pay), and the PO sits in the middle of it.

## What should a purchase order include?

A PO should answer every question the invoice will later be checked against. If something isn't on the PO, nobody can prove later that it was agreed.

| Field | Why it matters |
| --- | --- |
| PO number | The reference the vendor must quote on the invoice |
| Vendor name and address | Confirms who you are paying |
| Order date and delivery date | Sets expectations and catches late orders |
| Line items with quantity and unit price | The numbers the invoice is matched against |
| Total, tax and shipping | Stops surprise charges |
| Payment terms | For example Net 30, so the due date is agreed |
| Delivery or service address | Where the work happens or goods go |
| Approver | Shows the purchase was authorized |

Keep the description specific. "Office supplies" is hard to match. "20 boxes of copy paper, letter size, at $42.00 a box" is easy.

## Who provides a purchase order, the buyer or the seller?

The buyer creates and sends the purchase order. The seller replies with an acceptance, then later an invoice. That is the simplest way to keep the two documents straight: the PO asks for goods at an agreed price, and the invoice asks for payment for what was delivered. The [purchase order vs invoice](https://learn.ynteractive.com/content/glossary/purchase-order-vs-invoice) entry compares them side by side.

## How do you read a PO you received from a customer?

If you are the vendor, read a customer's PO against your own quote before you accept it. Check the PO number (you will need it on the invoice), each line's quantity and price, the delivery date, the payment terms and the billing address. If anything differs from what you quoted, say so before you ship, because once you accept, the PO terms usually govern the order.

## Where does AI fit in the purchase order process?

AI is good at the typing and the checking, and a person should still make the decisions. The useful jobs are:

- **Reading invoices.** In the [invoice approval lesson](https://learn.ynteractive.com/content/invoice-inbox-to-google-sheets-approval-n8n), an n8n workflow reads vendor invoice PDFs from Gmail, pulls out the vendor, invoice number and total, and logs every invoice in Google Sheets.
- **Routing approvals.** The same workflow sends anything over $1,000 to the owner, and nothing is approved until the owner clicks Approve in an email.
- **Categorizing spend.** The [AI Expense Categorizer Agent](https://learn.ynteractive.com/content/n8n-ai-agent-categorize-business-expenses-google-sheets) sorts business expenses into categories in Google Sheets, so the PO and the books tell the same story.
- **Chasing late orders.** A short, factual follow-up email to a vendor who has missed a delivery date is a good drafting job. [Purchase Order Follow-Up Email](https://learn.ynteractive.com/content/blog/purchase-order-follow-up-email) has a template.

## Try it free, step by step

**Invoices from Your Inbox to Google Sheets, with Approval**. Build an n8n workflow that reads each vendor invoice PDF from Gmail with AI, logs the vendor, invoice number and total in Google Sheets, and emails the owner an Approve button for anything over… You do every step yourself in a practice copy of n8n, it checks your work as you go, and “Do it for me” finishes any step you get stuck on. Free, and nothing touches your real accounts.

[Start the free lesson](https://learn.ynteractive.com/modules/invoice-inbox-approval)

[Or read the full step-by-step guide](https://learn.ynteractive.com/content/invoice-inbox-to-google-sheets-approval-n8n)

## Do small businesses need purchase orders?

Not for every purchase. Many small offices skip POs for small, routine spending and use them for large orders, new vendors or anything with a delivery to check. A simple rule written down, such as "a PO for anything over $1,000 or any new vendor," gives most of the control with little paperwork. For repeat orders with one vendor, a [blanket purchase order](https://learn.ynteractive.com/content/glossary/blanket-purchase-order) covers many deliveries under one agreement.

## Key takeaways

- A purchase order is the buyer's written order to a vendor, created after an internal request is approved.
- The usual steps are request, approve, create the PO, vendor accepts, receive, invoice, then match and pay.
- A PO should list the PO number, vendor, dates, line items with quantities and prices, totals and payment terms.
- Accounts payable pays only when the invoice matches the PO, and sometimes the receiving record too.
- AI can read invoices and route approvals, while a person still approves the spending.

## Frequently asked questions

**Is a purchase order legally binding?**

Once the vendor accepts it, a purchase order is generally treated as a contract for that order. The exact rules depend on your terms and where you do business, so have your standard PO terms reviewed if large amounts are involved.

**What happens if the invoice doesn't match the PO?**

Accounts payable holds the invoice and asks the vendor or the requester to explain the difference. Common causes are a price change, a partial delivery or an extra charge. Pay once the difference is agreed or the invoice is corrected.

**What is a PO number used for?**

The PO number links the order, the delivery, the invoice and the payment. Vendors quote it on the invoice so accounts payable can find the matching order quickly.

**Can a purchase order be changed after it is sent?**

Yes. Send a revised PO or a change order with the same PO number and a revision mark, and get the vendor to accept the change, so the invoice is matched against the latest version.

## Where can I go next?

Build the matching end yourself in [Invoice PDFs from Gmail to Google Sheets with n8n](https://learn.ynteractive.com/content/invoice-inbox-to-google-sheets-approval-n8n), then read [Get Receipts into Google Sheets with AI and n8n](https://learn.ynteractive.com/content/blog/receipts-to-google-sheets-ai) for the reading step.

## Free lessons in this post

- [Invoices from Your Inbox to Google Sheets, with Approval](https://learn.ynteractive.com/content/invoice-inbox-to-google-sheets-approval-n8n): Build an n8n workflow that reads each vendor invoice PDF from Gmail with AI, logs the vendor, invoice number and total in Google Sheets, and emails the owner an Approve…
- [Build an AI Agent That Categorizes Business Expenses](https://learn.ynteractive.com/content/n8n-ai-agent-categorize-business-expenses-google-sheets): Build an AI agent for Maple Street Bookkeeping that sorts business expenses into categories, writes a short note for each and saves them to Google Sheets — chat…

## Watch it in a free lesson: Invoices from Your Inbox to Google Sheets, with Approval

### Invoices from Your Inbox to Google Sheets, with Approval: video walkthrough

Full walkthrough · 2:31 · with captions

Build an n8n workflow that reads each vendor invoice PDF from Gmail with AI, logs the vendor, invoice number and total in Google Sheets, and emails the owner an Approve button for anything over $1,000. The whole lesson narrated step by step, recorded in Stepthrough’s simulated practice environment.

[Watch it with chapters and the full transcript](https://learn.ynteractive.com/content/invoice-inbox-to-google-sheets-approval-n8n#watch)

From the free lesson [Invoices from Your Inbox to Google Sheets, with Approval](https://learn.ynteractive.com/content/invoice-inbox-to-google-sheets-approval-n8n)

## Related terms

Plain-English definitions, each with an example from a free lesson.

[Purchase order](https://learn.ynteractive.com/content/glossary/purchase-order) · [Accounts payable](https://learn.ynteractive.com/content/glossary/accounts-payable) · [Invoice](https://learn.ynteractive.com/content/glossary/invoice) · [A/B testing](https://learn.ynteractive.com/content/glossary/ab-testing) · [AI agent](https://learn.ynteractive.com/content/glossary/ai-agent) · [AI data entry](https://learn.ynteractive.com/content/glossary/ai-data-entry) · [AI evals](https://learn.ynteractive.com/content/glossary/ai-evals) · [AP aging report](https://learn.ynteractive.com/content/glossary/ap-aging-report)

[The full AI glossary](https://learn.ynteractive.com/content/glossary)

## Related prompts

- [AI pilot plan prompt](https://learn.ynteractive.com/content/prompts/ai-pilot-plan-prompt): Plan a small, time-boxed trial of an AI tool: one task, a few people, success criteria you choose up front, how you'll measure…
- [Case study interview questions prompt](https://learn.ynteractive.com/content/prompts/case-study-interview-questions-prompt): Plan a client interview that gets a case study's before, during and after story in their own words, with follow-up probes and…
- [Duplicate invoice check prompt](https://learn.ynteractive.com/content/prompts/duplicate-invoice-check-prompt): Scan the bills in a payment run for likely duplicates: same vendor and amount, near-matching invoice numbers and bills already…
- [Email subject lines prompt](https://learn.ynteractive.com/content/prompts/email-subject-lines-prompt): Get ten honest subject lines for a finished email, each with preview text and a character count, grouped by approach so you can…

[All free prompt templates](https://learn.ynteractive.com/content/prompts)

## Visual guides

The same ideas as quick visual guides: swipe through the slides, or read each one as text.

- [5 Steps to an AI Agent That Categorizes Business Expenses](https://learn.ynteractive.com/content/visual/5-steps-ai-expense-categorizer): A visual guide: an n8n agent sorts expenses into a fixed list of categories, flags unclear ones as Needs Review and saves them to Google Sheets.
- [Mistake to Avoid: Letting AI Invent Expense Categories](https://learn.ynteractive.com/content/visual/mistake-letting-ai-invent-categories): A visual tip for bookkeepers: give an AI agent a fixed list of categories plus Needs Review, so it never makes up a category name.

[All visual guides](https://learn.ynteractive.com/content/visual)

## Keep reading

- [How to Add AI to Finance Workflows Without Rebuilding](https://learn.ynteractive.com/content/blog/how-to-add-ai-to-finance-workflows): The most effective ways to add AI to existing finance workflows: start with exports, add one AI step to the inbox you have, and keep people on approvals.
- [What to Check Before AI Auto-Approves Invoices](https://learn.ynteractive.com/content/blog/what-to-check-before-ai-approves-invoices): What to check before letting an AI agent auto-approve invoices or expenses: duplicates, vendor and bank details, PO match, limits, math and an audit log.
- [What Is a Chart of Accounts? Give Your AI the Categories](https://learn.ynteractive.com/content/blog/what-is-a-chart-of-accounts): A chart of accounts is the list of accounts your books use. What it is, why AI expense tools need yours, and how to put it into an n8n agent's prompt.

[All blog posts](https://learn.ynteractive.com/content/blog) · [All free tutorials](https://learn.ynteractive.com/content)