Automate Overdue Invoice Reminders with n8n, Gemini, Gmail & Slack

Automate Overdue Invoice Reminders with n8n, Gemini, Gmail & Slack

Stop chasing overdue payments manually. This n8n workflow checks your unpaid invoices in Google Sheets, uses Google Gemini to draft stage-appropriate reminder emails, sends them via Gmail, optionally notifies Slack for long-overdue cases, and updates the sheet so reminders continue correctly.

What this workflow does

• Runs daily at 09:00 to keep reminders consistent.
• Reads invoice rows from the Google Sheets “Invoices” sheet.
• Calculates overdue status by computing how many days each invoice is overdue and how long it’s been since the Last Reminder.
• Assigns a reminder stage (gentle, firm, or escalate). If an invoice is not due or the last reminder was too recent, it skips sending.
• Generates the email body with Google Gemini, matching the tone to the selected stage, and sends via Gmail with a subject line tailored to that stage.
• Escalates via Slack for “escalate” invoices: after sending the final notice, it posts an alert to your chosen #finance channel.
• Updates Google Sheets with the latest reminder details (including a new reminder timestamp) so the sequence can continue on the next run.

Use cases

• Keep SaaS billing teams focused by automating reminders for invoices that remain unpaid.
• Use gentle-to-escalation messaging to reduce payment friction while still applying pressure over time.
• Ensure finance visibility: automatically alert Slack when an invoice reaches the “escalate” stage.

Technical details

• n8n schedule: daily at 09:00
• Integrations / nodes: Google Sheets, Google Gemini (PaLM) API, Gmail, Slack, plus workflow logic using Code, Switch, and Sticky Note nodes
• Required columns: Invoice No, Client, Contact Email, Amount, Due Date, Last Reminder (use consistent, parseable date formats)