LINE Receipt Expense Capture with Gemini, Drive & Sheets (n8n)

Capture LINE receipt expenses automatically—Gemini extraction, Japanese invoice T-number validation, and Google Sheets logging via n8n

This n8n workflow listens for receipt photos sent through LINE, extracts structured expense details with Google Gemini, verifies Japanese invoice T-numbers using the NTA Web-API, then archives the image to Google Drive and records the expense in Google Sheets. The user gets a confirmation reply back in LINE.

What this workflow does

• Receives a POST webhook from LINE and reads the message type, message ID, reply token, and user ID.
• If the event is not an image, it replies in LINE instructing the user to send a receipt photo.
• For image messages, it downloads the image from LINE, uploads it to Google Drive, and converts the file to Base64.
• Sends the image to Google Gemini to determine whether it’s a receipt and to extract: receipt date, vendor, totals, tax, category, description, and any T-number.
• If Gemini indicates it’s not a receipt, it asks the user (via LINE) to retake and resend the photo.
• If a T-number is present, it calls the NTA invoice validity endpoint using the extracted receipt date, then combines the validity result with the extracted expense data and the Google Drive file link.
• Appends the final record to Google Sheets and replies in LINE with the invoice validity status.

Use cases

• Teams collecting receipt photos on mobile and auto-generating expense logs with invoice validity checks.
• SaaS operators automating back-office bookkeeping steps without manual spreadsheet entry.
• n8n users building a chat-based expense capture pipeline for Japanese invoices.

Technical details

• LINE Messaging API: webhook trigger, image download, and LINE reply using Channel Access Token.
• Google Gemini: receipt classification and structured field extraction (configurable endpoint/model as needed).
• NTA Web-API: T-number invoice validity verification.
• Google Drive: image archive and Drive link storage.
• Google Sheets: expense record appending.
• Core n8n logic uses nodes such as webhook, if, code, set, merge, and supporting workflow components.