Gmail Invoice OCR to Google Sheets + Slack Reminders (n8n)

Turn invoice emails into a tracked spreadsheet—and send due-date reminders automatically

This n8n workflow monitors your Gmail inbox for invoice PDFs, extracts invoice details with OpenAI, records them in Google Sheets with duplicate detection, and then sends daily payment reminders via Gmail plus real-time alerts to Slack.

What this workflow does

• Checks for new invoices hourly: Triggers every hour when a Gmail message arrives in Inbox with an attachment and a subject containing “invoice” or “bill.”
• Extracts invoice data from the PDF: Downloads the attachment, extracts text from the PDF, and sends it to OpenAI to return structured JSON (vendor name, invoice number, amount, due date).
• Detects duplicates automatically: Searches your Google Sheets tracker for an existing row matching the extracted invoice number.
• Alerts on duplicates: If found, posts a duplicate invoice alert message to a configured Slack channel.
• Tracks new invoices: If not found, appends a new row to Google Sheets with a default Pending status and a created timestamp.
• Sends reminders daily at 9:00: Loads invoice records from Google Sheets, calculates days remaining until the due date, assigns reminder type and priority, and for invoices requiring action sends:
  • Payment reminder emails via Gmail (to a configured recipient)
  • Reminder messages via Slack
• Updates statuses: Modifies invoice status in Google Sheets (for example, marking overdue invoices as OVERDUE).

Use cases

• AP teams who receive vendor invoices by email and want a live invoice tracker with due-date follow-ups.
• SaaS operators who want fewer missed payments by combining Google Sheets logging with Gmail + Slack reminders.
• Automation engineers deploying an invoice ingestion pipeline in n8n using OpenAI-powered extraction.

Technical details

• n8n trigger: Gmail (Inbox monitoring for subjects containing “invoice”/“bill” with attachments)
• Extraction: PDF text extraction + OpenAI returning structured JSON
• Deduplication & logging: Google Sheets lookup and append, with default “Pending” status
• Notifications: Slack duplicate alerts and reminder posts
• Email reminders: Gmail send step at 9:00 daily
• Core workflow logic: nodes such as if, set, and code (plus Sticky Note for guidance)

Requires connecting your Gmail credentials for both reading and sending, and adding an OpenAI API credential for the invoice field extraction.