n8n Slack Invoice Extraction with Gemini, Drive & Sheets

Automatically extract invoice data from Slack uploads—then archive, log, and summarize in one thread

With this n8n Slack invoice extraction workflow, invoices posted in a Slack channel are automatically downloaded, processed with Google Gemini, archived to Google Drive, recorded in Google Sheets, and summarized back in the original Slack thread—ready for faster bookkeeping and review.

What this workflow does

• Listens in Slack for new messages in a specified channel.
• Downloads the first attachment from the Slack message and normalizes it for processing.
• Validates file type: supports PDF and common image types. If the attachment isn’t supported, the workflow replies in the same Slack thread with an “unsupported file” notice.
• Extracts invoice fields with Gemini by sending the document to the Google Gemini API using a structured JSON schema prompt.
• Parses and validates results: generates a Markdown invoice summary and flags missing or inconsistent values for review.
• Archives the original invoice in a chosen Google Drive folder and combines the Drive link with the extracted invoice data.
• Logs to Google Sheets by appending invoice fields and the Drive file link.
• Replies back in Slack with the summary and archive link in the original thread.

Use cases

• Operations teams receiving supplier invoices in Slack and needing structured extraction for follow-up.
• SaaS operators who want automatic invoice data capture with Drive archiving and Sheets logging.
• Automation engineers building document processing workflows with Slack, Gemini, Drive, and Sheets.

Technical details

• Slack Trigger for new messages and attachment handling
• if and code nodes for supported-format checks and Gemini response parsing/validation
• HTTP Request to call the Generative Language API (Gemini) using API key authentication via HTTP header
• Google Drive to upload and generate shareable links
• Google Sheets to append extracted invoice fields and Drive URLs
• Includes merge to combine extracted data with the Drive link before writing to Sheets and replying in Slack