Gmail Invoice Automation with n8n, GPT-4.1-mini, Sheets & Drive

Automatically capture invoices from Gmail, extract data with GPT-4.1-mini, and log everything to Google Sheets + Drive

This n8n workflow scans your Gmail daily for unread invoice/receipt emails, uses GPT-4.1-mini to classify the message and extract structured fields (including text from the first attached PDF), then saves PDFs to Google Drive and records invoice activity in Google Sheets. You also get a daily digest email summary.

What this workflow does

• Runs every day at 7 AM on a schedule.
• Reads existing rows from Google Sheets to track previously processed invoices.
• Fetches unread Gmail messages and converts each email body to plain text.
• Extracts PDF text from the first attached PDF (when present) and merges email + PDF text into a single analysis payload.
• Calls OpenAI (GPT-4.1-mini) to classify the message as invoice/receipt/other and extract structured invoice/receipt fields.
• Deduplicates and updates records: compares extracted invoices against existing Google Sheets entries, matches receipt emails to unpaid invoices, and decides whether to append new rows or mark invoices paid.
• Uploads attachments to Google Drive (when required) and records resulting file links.
• Marks Gmail messages as read, applies a processed label, updates Google Sheets, and sends a formatted daily digest via Gmail.

Use cases

• AP/finance teams who receive invoices and receipts by email and need a reliable system of record.
• SaaS operators tracking billing with Google Sheets as a lightweight ledger.
• Automation engineers building an invoice data extraction pipeline that combines email parsing + PDF handling + spreadsheet logging.

Technical details

• Scheduled trigger (daily at 7 AM).
• Nodes/logic includes: if, set, code, gmail, merge, filter.
• Integrations: Gmail, Google Sheets, Google Drive, and OpenAI with GPT-4.1-mini.
• Requires: Gmail/Google credentials + an OpenAI credential connected to the extraction chain after importing.