How to set up a supplier-invoice approval pipeline from Gmail with n8n

Finance & invoicingn8n

The problem

Supplier invoices arrive by email and each one needs data extraction, duplicate and supplier checks, approval for larger amounts and an accounting entry.

Tools needed

• n8n (queue mode)
• PostgreSQL
• Redis
• Docker
• Gmail
• OCR
• OpenAI
• Slack

Step-by-step recipe

1. Run n8n in queue mode with PostgreSQL, Redis and a worker in Docker.
2. Create tables for suppliers, invoices and an audit log, and add Gmail, OpenAI, Postgres and Slack credentials.
3. Plan the flow: Gmail, then OCR, then AI extraction.
4. Then duplicate and supplier checks, classification, and approval routing for high-value invoices.
5. Finally create the journal entry and schedule the payment.

Copyable prompt

Classify this supplier invoice for accounts payable. Return JSON:
{"supplier_name": "...", "supplier_vat_id": "..."|null, "invoice_number": "...", "invoice_date": "YYYY-MM-DD", "due_date": "YYYY-MM-DD"|null, "net": number, "tax": number|null, "gross": number, "currency": "...", "expense_category": one of [CATEGORIES], "needs_approval": true if gross > [THRESHOLD]}
Use null when a value is not on the document.

Text: {{ocr_text}}

What the builder reported

This is part 1 of a three-part series and covers the infrastructure only. It ends with the stack and schema running; extraction, validation, approval and accounting are left to later parts. No results yet.

These are the source author's own claims. AgentRecipes has not tested or verified them.

Watch out for

• Queue mode can retry stalled jobs, so every step must be idempotent; duplicate detection is essential.
• Back up the n8n encryption key, or you lose access to stored credentials.

Source

More finance & invoicing recipes