Why this matters
Vendor invoices arrive as PDFs. Someone copies the vendor, invoice number and total into a spreadsheet by hand, then chases the owner for a yes on the big ones. It is slow, typos slip in, and a large invoice can get paid because nobody asked.
AI can read the PDF and fill the sheet in seconds. But AI can misread a scan, and nobody wants software deciding to pay $12,000 on its own. The answer is a human approval step: the workflow does the reading and the logging, then stops and waits for a person to approve anything over a set amount.
That pattern, AI does the work and a named person signs off above a threshold, is the core of human review in any AI governance plan. You build it here for invoices, and the same shape works for client emails, refunds and anything else AI drafts.
What you’ll build
You keep the books at Cobalt Street Architects, a made-up firm. The workflow already catches invoice emails and turns each PDF into text. You add an Information Extractor that pulls out the vendor, invoice number, dates and total without guessing, log every invoice with Google Sheets Append row in sheet, and add an If node: total greater than 1000.
On the true branch, Gmail Send message and wait for response emails the owner, Lena, an Approve button and pauses the workflow until she answers. You run it on a pinned Tidewater Office Supply invoice for $1,284.50: the row lands in the sheet and Lena gets the approval email.
What you need
- Nothing to start the practicen8n, Gmail and Google Sheets are practice copies. No email is read or sent and no sheet changes.
- n8n, to do it for realn8n Cloud or your own n8n.
- An OpenAI API key with a little creditFor the Information Extractor’s OpenAI Chat Model. Keys are created at platform.openai.com.
- Gmail and Google Sheets connected in n8nA sheet with Vendor, Invoice # and Total columns, and the approver’s email address.
- Your approval thresholdThe amount above which a person must approve. The lesson uses $1,000.
Concepts
3 ideas you’ll use in the practice.
AI reads, a person decides
The extractor’s instructions say: copy what is printed, never calculate or guess, and leave a field empty rather than invent it. That keeps the AI step narrow.
The decision to pay stays with a person. Send message and wait for response pauses the workflow until the owner clicks Approve, so nothing over the threshold moves without a yes.
A threshold keeps review practical
If a person has to approve everything, they stop reading and click yes. A threshold, here $1,000, means small items flow through and are logged, while the ones that matter get real attention.
The sheet is your record
Every invoice is logged before the approval step, so you have a record of what came in, what the AI read and what was sent for approval. Spot-check the first invoices against the PDFs, and add a column for the decision if you need a fuller audit trail.
Practice
Do every step yourself in a practice copy of the real tool. It checks your work, and “Do it for me” finishes any step you get stuck on.
Do it for real
Now repeat it in your own account. Tick each step as you go.
Quick check
3 questions to check you’ve got it.
1. Why does the extractor say "don’t calculate or guess"?
- To make it faster
- So it copies what is printed and leaves a field empty instead of inventing it
- n8n requires it
Show the answer
So it copies what is printed and leaves a field empty instead of inventing it. An empty field is easy to spot. A made-up number is not.
2. What does Send message and wait for response do?
- Pays the invoice
- Emails an Approve button and pauses the workflow until the person answers
- Deletes the email
Show the answer
Emails an Approve button and pauses the workflow until the person answers. It is the human approval gate: nothing on that branch continues without a yes.
3. Why use a threshold instead of approving every invoice?
- So reviewers give real attention to the ones that matter
- Because small invoices are never wrong
- To hide small invoices
Show the answer
So reviewers give real attention to the ones that matter. Approving everything turns review into clicking yes. Small items are still logged.