n8n AI Invoice Reply Classifier: Claude Haiku + Gmail + Sheets

Turn invoice email replies into instant, triaged categories—using Claude Haiku + Gmail + Google Sheets

This n8n workflow automatically watches your Gmail for replies to invoice reminders, uses Claude Haiku to classify each response (Paid, Promise, Dispute, Question, or Unrelated), then logs the result to Google Sheets and applies the matching Gmail label so you can act fast.

What this workflow does

• Monitors Gmail for new invoice replies using a configurable search (default: emails with “invoice” in the subject, excluding messages sent by you).
• Cleans the reply text by stripping quoted history and signatures to improve AI classification accuracy.
• Classifies with Claude Haiku into one of: Payment made, Promise to pay, Dispute, Question, or Unrelated. For promises, it extracts a promised payment date and provides a one-line reason.
• Logs to Google Sheets, including a direct link back to the Gmail thread for quick context.
• Labels the Gmail message so you can immediately triage: the corresponding category label, or Needs review if the model fails (with the error recorded).

Use cases

• Invoice reminder inbox management for SaaS operators who need rapid follow-ups on paid vs promised vs disputed replies.
• Accounts receivable automation: instantly sort inbound replies and capture structured outcomes in Google Sheets.
• Customer support triage: route Question and Unrelated responses without manually reading every thread.

Technical details

• Integrations: Gmail, Google Sheets (via Google OAuth; self-hosted n8n requires a Google Cloud app).
• AI: Claude Haiku 5.5 node for reply classification.
• n8n nodes used: set, code, gmail, merge, switch, sticky note.
• Gmail labels required: Payment made, Promise to pay, Dispute, Question, Unrelated, Needs review.
• Setup: provide the blank Google Sheet URL; the workflow writes the header row on the first run and you can adjust the Gmail search query to match your invoice reminder titles.