n8n Workflow: Numbered PDF Invoices from Gmail w/ Claude & Sheets

Turn invoice request emails into numbered, validated PDF invoices—automatically

This n8n workflow polls your Gmail inbox for invoice/order requests, extracts billing details with Anthropic Claude, validates totals, assigns a sequential yearly invoice number in Google Sheets, generates an A4 PDF via MintPDF, replies to the customer with the PDF, and logs everything back to Sheets—while archiving the PDF in Google Drive.

What this workflow does

• Monitors Gmail every minute: checks unread emails with subjects matching invoice or order request patterns.
• Extracts structured invoice data: uses Anthropic Claude to pull customer, billing details, and line items from the email.
• Validates and calculates totals: ensures required fields and currency are present, calculates subtotal, tax, and total in integer cents, and routes invalid or over-limit requests to a Google Sheets “Review” tab (and emails the owner).
• Avoids duplicates + assigns numbering: reads an invoice log in Google Sheets to skip already-invoiced emails, then assigns the next invoice number for the year.
• Renders a PDF invoice: converts escaped HTML into an A4 PDF using MintPDF; if rendering fails, emails the owner.
• Customer reply + archiving: archives the PDF to Google Drive, replies in the original Gmail thread with the PDF attached, and appends invoice details and the Drive link to the Sheets log.

Use cases

• SaaS operators who receive ad-hoc invoice requests by email and need consistent numbering and PDFs.
• Small businesses sending invoices manually but wanting an automated Gmail → Claude → Sheets → MintPDF pipeline.
• Teams that need a review queue for invalid totals or missing fields before invoicing.

Technical details

• Node/stack: if, set, code, no op, merge (plus required community node for PDF generation).
• Integrations: Gmail, Google Sheets, Google Drive, Anthropic (Claude).
• MintPDF: install community node n8n-nodes-mintpdf and add a MintPDF API credential.
• Google Sheets tabs: Invoices and Review, with columns matching the fields appended by the workflow.