Invoice Data Extraction with OpenAI, Gmail & Google Sheets

Extract invoice data automatically with OpenAI, track it in Google Sheets, and send Gmail alerts

This n8n workflow receives invoice uploads via a webhook, uses OpenAI to extract structured fields, detects duplicates in Google Sheets, and sends Gmail notifications for duplicate or low-confidence invoices—then posts clean invoices to your accounting system via an HTTP request.

What this workflow does

• Receives invoice files through a webhook endpoint and validates the uploaded file type.
• Extracts text from PDFs to prepare invoice content for parsing.
• Uses OpenAI to extract invoice fields such as vendor, invoice number and dates, totals, currency, and line items.
• Checks Google Sheets for duplicates by comparing vendor name and invoice number within the “Invoices” tab.
• Validates line-item totals against the extracted invoice total and flags low-confidence extractions for review.
• Sends Gmail status emails when duplicates are found or when manual review is needed.
• Posts non-flagged invoices to your accounting software using a configurable HTTP request, appends the record with status to Google Sheets, and responds to the webhook with a JSON “received” message.
• Runs daily at 8:00 AM to read the Google Sheets log, filter invoices marked “review,” and email you a reminder list via Gmail.

Use cases

• Automate invoice intake for SaaS operations where invoices arrive as PDF attachments.
• Prevent double-entry by detecting duplicates in an “Invoices” Google Sheets log.
• Speed up AP review by emailing only duplicates and low-confidence extractions for human validation.
• Push confirmed invoice data to an accounting system through an HTTP endpoint.

Technical details

• Webhook for file upload intake and JSON “received” responses
• OpenAI for structured invoice extraction
• Google Sheets OAuth2 to read/write the “Invoices” tab and track status
• Gmail OAuth2 for duplicate alerts, review requests, and daily reminders
• Workflow logic with if, set, code, plus supporting steps (including sticky notes)

Setup requires OpenAI, Google Sheets OAuth2, and Gmail OAuth2 credentials, plus configuration of your owner email and the Google Sheets document ID with an “Invoices” tab containing the required columns.