Invoice monitor
Diagram of the Invoice monitor system: 6 steps
Steps
- Invoice arrives: A supplier invoice arrives as a PDF attachment.
- Reads the PDF: Supplier, amount, date and order number are pulled from the PDF.
- Matches the order: The invoice is matched to the order in the expense sheet.
- Amount differs?: The amount is compared with what was ordered.
- Pre-booked: A matching invoice is recorded and ready for approval.
- Asks a person: A person is asked before anything is recorded.
Each invoice checked against its order; a gap over 2 % goes to a person
The problem
Supplier invoices arrive as PDFs in a shared inbox. Somebody opens each one, finds the matching order, compares the amount, and enters the invoice into the expense sheet or the accounting tool. At 10 to 15 minutes per invoice, a company that receives 40 invoices a week spends about a working day on it, most of it on invoices that are simply correct. The dangerous ones are the few that are not: a price that changed, a quantity that does not match, a duplicate. Those get missed exactly when the pile is tallest. We built this demo to show the pattern we recommend for it.
The system
Gmail is the trigger: a new email with a PDF attachment under the invoices label. Claude reads the PDF and pulls out supplier, invoice number, date, line items and total. The n8n workflow looks up the matching order in a Google Sheet by supplier and order number. If the total is within 2 % of the order, the invoice is pre-booked: a row in the expense sheet with the file linked, marked as checked by the system. If the amount differs by more than 2 %, no order is found, or the invoice number has been seen before, the workflow stops and posts the invoice to Slack with the reason and both amounts side by side. A person approves, rejects or corrects it from there.
What it does now
In the demo, every invoice is read and matched without a person, and the held ones wait in Slack with the reason attached. Nothing is paid or booked by the system: it prepares the row, and the person's approval is what writes it. The 2 % threshold, the label and the sheet are settings. Swapping the sheet for an accounting tool with an API is the usual first change for a client.
Where AI checks and where it decides
| Step | Who decides |
|---|---|
| Reading the PDF and matching it to an order when the amounts agree within 2 % | AI decides |
| Every invoice that differs, every duplicate, every unknown supplier, and any payment | A person decides |