n8n Xero Overdue Invoice Reminders: Gmail + Slack + Sheets

Automate Xero overdue invoice reminders—daily, tiered, and logged

This n8n workflow pulls unpaid invoices from Xero every morning, calculates how many days they’re overdue, then sends tiered Gmail reminders and Slack alerts—while recording each reminder in Google Sheets to prevent duplicate follow-ups.

What this workflow does

• Runs daily at 08:00 using a scheduled trigger.
• Loads overdue thresholds (7, 14, 30 days) and fetches unpaid invoices from your selected Xero organisation.
• Calculates days overdue for each invoice and assigns it to a 7-, 14-, or 30-day tier.
• Generates a unique identifier invoiceId_tier and prepares key fields such as contact email and amount due.
• Checks Google Sheets log to see whether that exact invoiceId_tier has already been processed; if it has, the workflow skips it.
• 7-day overdue: sends a friendly Gmail reminder to the customer.
• 14-day overdue: sends a firmer Gmail reminder and posts an internal Slack alert.
• 30-day overdue: posts a Slack escalation message that includes a call task, then logs the processed invoiceId_tier entries back to Google Sheets.

Use cases

• Reduce manual follow-up for customers with outstanding invoices in Xero.
• Give your team early visibility at 14 days and escalation workflow at 30 days.
• Maintain a reliable audit trail of reminders so customers aren’t spammed with repeated messages.

Technical details

• Integrations/nodes: Xero, Gmail, Slack, Google Sheets (plus if, set, code, merge).
• Authentication: OAuth credentials for Xero, Gmail, and Google Sheets.
• Prerequisites: Xero contacts must include an email address so reminders have a valid recipient.
• Sheets requirement: a tab containing an invoiceId_tier column for de-duplication.