n8n Workflow: 3-Way Match Vendor Invoices in Google Sheets + Gmail Alerts

Automate PO/GRN/Invoicing 3-Way Matching with Google Sheets + Gmail alerts

This n8n workflow automatically captures vendor invoice submissions, checks Google Sheets for duplicates, performs PO/GRN/invoice 3-way match against your reference data, and sends Finance-ready or exception notifications via Gmail.

What this workflow does

• Receives invoices via an n8n form trigger (vendor invoice submission).
• Normalizes key fields such as Vendor ID, Invoice Number, PO, GRN, and item code, then generates a unique invoice key.
• Prevents duplicate invoices by searching the Google Sheet tab “Invoice Register” for an existing row with the same Vendor ID + Invoice Number. If a duplicate is found, it sends an email to the submitter using Gmail.
• Registers valid invoices by appending them to “Invoice Register” with status PENDING_MATCH.
• Performs 3-way matching against Google Sheets reference data from “Purchase Orders” and “Goods Receipts” using PO/GRN number and item code.
• Validates approvals and consistency, including checks for receipt status, vendor/item/currency consistency, and quantity/price/total validation.
• Updates status and alerts Finance in “Invoice Register”:
  • READY_FOR_PAYMENT (and emails Finance via Gmail), or
  • PAYMENT_HOLD with exception reasons (and emails Finance via Gmail).

Use cases

• Accounts Payable teams routing vendor invoices for faster review with consistent PO/GRN checks.
• SaaS operators consolidating invoice intake into Google Sheets while using Gmail to notify Finance of readiness vs. holds.
• Automation engineers standardizing duplicate prevention and exception handling in an n8n workflow.

Technical details

• n8n Form Trigger to collect vendor invoices
• Google Sheets integration for reading/writing tabs: Invoice Register, Purchase Orders, Goods Receipts
• Workflow logic using if, set, and code
• Gmail node for submitter and Finance notifications
• Uses a unique invoice key and status values: PENDING_MATCH, READY_FOR_PAYMENT, PAYMENT_HOLD

Setup requires adding Google Sheets credentials and updating YOUR_GOOGLE_SHEET_ID for the Invoice Register, Purchase Orders, and Goods Receipts queries/updates.