Gmail Invoice Auto-Classification with OpenAI & Google Sheets (n8n)

Auto-classify your Gmail invoices and book entries into Google Sheets—powered by OpenAI (n8n)

This Gmail Invoice Auto-Classification with OpenAI & Google Sheets (n8n) workflow scans your inbox every hour, uses OpenAI to classify unread emails (sales, expense, settlement, transaction, notification, other), extracts key invoice/payout fields, stores PDFs in Google Drive, and logs everything into Google Sheets—then labels and marks messages as read.

What this workflow does

• Runs hourly: fetches all unread Gmail messages on a schedule.
• Classifies each email with OpenAI based on the email subject and body into: sales, expense, settlement, transaction, notification, or other.
• Expense emails: extracts invoice fields (e.g., vendor, invoice number, GST split, amounts, and payment details). It also fetches any PDF attachment from Gmail, uploads it to Google Drive, and appends a linked row to the Expense tab in Google Sheets.
• Sales emails: extracts order details, generates an HTML sales confirmation, renders it to PDF with PDFBolt, uploads the PDF to Google Drive, and appends a linked row to the Sales tab in Google Sheets.
• Settlement emails: extracts payout details, uploads any PDF attachment to Google Drive, and appends a linked row to the Settlement tab in Google Sheets.
• Transaction/notification/other: applies the corresponding Gmail label and marks the message as read.
• Error handling: on failures, an error trigger uses OpenAI to translate the technical error, and alerts via Discord and Gmail.

Use cases

• Automatically turn vendor invoice emails into structured rows for accounting visibility in Google Sheets.
• Track sales confirmations by generating and storing PDFs while keeping order data synchronized in Sheets.
• Centralize settlement documentation (with PDFs) for easier monthly reconciliation.

Technical details (n8n)

• Integrations/nodes: Gmail, OpenAI, Google Sheets, Google Drive, Discord, PDFBolt
• Flow building blocks: if, code, switch, split out