Flag possible duplicate vendor invoices (n8n)

Once a week, scan recent bills for the same vendor and amount, or the same invoice number, and email a list of suspects.

n8nAccounts payableIntermediateHuman check: Medium

Tools
n8n: QuickBooks Online, Google Sheets, Gmail

Time saved
~1-2 hrs/month (estimate)

Difficulty
Intermediate

Steps

Schedule Trigger: weekly.
QuickBooks Online → Bill → Get All (or Transaction → Get Report) for the last 90 days.
Code node: group by vendor + total + DocNumber and keep the groups with more than one bill.
Write the results to Google Sheets (Append Row) as a review log.
Gmail → Send a message with the suspect list if it isn't empty.

Keep a human check here: Medium risk

The flag is only a warning. Look at both bills yourself before you void or delete either one.

Node and module names match n8n's docs as of Oct 2026. Apps rename triggers and actions sometimes, so check yours in the editor. Try it with test data or a sandbox company first.

Build it

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