n8n Workflow: Send Quotes & Invoices from Google Sheets via Gmail

Send quotes, invoices, and receipts from Google Sheets—automatically with Gmail

This n8n workflow watches your Google Sheets jobs tracker and, based on each row’s stage, generates the correct document PDF via Koutei and emails it through Gmail—also sending overdue invoice reminders and writing back delivery/validation issues to the sheet.

What this workflow does

• Runs on schedule: a manual trigger, every 30 minutes, and an additional run every morning at 9:00 to handle reminder emails.
• Reads your Google Sheets tab: loads all rows, evaluates each row’s stage and required fields, and decides whether to send a quote, deposit invoice, balance invoice, or receipt.
• Prevents duplicate sends: when a document is requested, it marks the row as “Sending…” before processing.
• Generates PDFs via Koutei: validates document data with Koutei, then requests the final PDF using an idempotency key to avoid duplicate document creation on retries.
• Sends emails using Gmail: emails the generated PDF to the appropriate recipient in the correct mode (owner in preview mode; client in final mode).
• Updates tracking in Google Sheets: writes back the new stage, totals, due date, email ID, and other status fields for auditing and workflow continuity.
• Automated overdue reminders: on the daily reminder run, finds overdue deposit or balance invoices, re-downloads the original sent attachment from Gmail, and emails a reminder with the same PDF—updating reminder tracking fields.
• Error handling with visibility: if validation, PDF generation, emailing, or sheet updates fail, it records an actionable status note in the relevant row and emails the owner.

Use cases

• Your operations team updates a “jobs” Google Sheet stage, and the system sends the right quote/invoice/receipt without manual steps.
• Invoices that become overdue automatically trigger reminder emails using the original PDF attachment from Gmail.
• Automation engineers want reliable idempotency and traceable status notes when Koutei validation or Gmail delivery fails.

Technical details

• n8n nodes: if, set, code, no op, Gmail, filter.
• Integrations: Google Sheets for the jobs tracker, Gmail for sending and retrieving attachments, and Koutei for document generation and validation.