Approve Supplier Invoices: Gmail + GPT-4o-mini, Sheets & Telegram

Automatically approve (or flag) supplier invoices from Gmail PDFs—using GPT-4o-mini, Google Sheets, and Telegram

This n8n workflow monitors your Gmail inbox for unread invoice emails with PDF attachments, extracts invoice details with GPT-4o-mini, verifies vendors and duplicates in Google Sheets, and routes approvals through Telegram—then records results and sends a weekly payment run summary.

What this workflow does

• Runs every minute: triggers when a new unread Gmail email with a PDF attachment is found.
• Extracts invoice text: pulls text from the PDF attachment.
• Uses GPT-4o-mini for structured parsing: sends email context + extracted PDF text to OpenAI (GPT-4o-mini) and parses the result into a fixed invoice JSON schema.
• Checks vendor + duplicates in Google Sheets:
  • Looks up the supplier in the Sheets tab “Vendors”.
  • Checks the tab “Bills” for an existing record with the same vendor and invoice number.
• Applies auto-approval rules: auto-approves only when the vendor is known, it’s not a duplicate, it meets the confidence threshold, and it’s under the configured auto-approve limit.
• Routes exceptions via Telegram: flags duplicates, unknown vendors, and invoices that exceed limits or have low confidence for Approve/Reject via Telegram with a 3-day timeout.
• Updates records + notifies finance: appends invoice decision and notes to “Bills”, marks the Gmail email as read, and notifies finance on Telegram for non-approved outcomes.
• Weekly payment run (every Monday 08:00): reads approved unpaid bills due now or within 7 days, emails an HTML payment run list via Gmail, and updates rows with a PaymentRun ID.

Use cases

• AP teams want faster invoice triage without losing control of approvals.
• SaaS operators reduce manual checking of vendor lists, invoice numbers, and duplicate detection.
• Finance teams need Telegram-based decision workflows with an explicit timeout for exceptions.

Technical details

• n8n nodes/integrations: Gmail, OpenAI (GPT-4o-mini), Google Sheets, Telegram
• Logic components: if, set, code, no op, merge (for routing decisions and JSON schema handling)
• Primary sheets: Vendors (supplier lookup) and Bills (decisions, duplicates, PaymentRun updates)