Gmail & Google Drive Invoice Processing with Gemini, Slack & Sheets

Automate Invoice Processing from Gmail & Google Drive—With Gemini, Slack approvals, and Google Sheets ledgers

This n8n workflow automatically detects new invoice and receipt files in Gmail and a Google Drive folder, extracts structured data with Google Gemini, logs results into Google Sheets, and sends higher-value invoices to Slack for approve/reject decisions—then updates your ledger automatically.

What this workflow does

• Runs every minute to check for new unread Gmail messages with invoice/receipt attachments and for newly created files in a specified Google Drive folder.
• Filters by file type: processes only PDFs and images. Unsupported items are marked as read, and a Slack notification is sent when a file type is skipped.
• Extracts invoice fields with Gemini: sends each supported document to Google Gemini, parses and validates the JSON output, and posts to Slack if extraction is incomplete or totals don’t reconcile.
• Prevents duplicate ledger entries: checks Google Sheets for an existing row using the invoice number. If found, it skips logging and notifies Slack about the duplicate.
• Categories and approval routing: uses Gemini to assign an expense category, then compares the invoice total against a threshold.
• Ledger actions: appends under-threshold totals as Approved, while over-threshold totals are logged as Pending Review with Slack Approve/Reject buttons.
• Decision handling: waits up to three days for the Slack response, then updates the matching Google Sheets row to Approved, Rejected, or No Response. Errors trigger a Slack alert.

Use cases

• Turning email receipts into an audit-ready expense ledger without manual copy/paste.
• Automatically routing invoices over a spend limit to Slack for approval workflows.
• Consolidating invoices from both Gmail attachments and Google Drive uploads.

Technical details

• Integrations / nodes: Gmail, Google Drive, Google Gemini, Slack, Google Sheets
• Workflow logic nodes: if, set, code, merge