Automate Overdue Invoice Chasing: n8n, Google Sheets, OpenAI & Gmail Drafts

Automate Overdue Invoice Chasing with n8n + Gmail Drafts (OpenAI-Assisted)

Stop manually following up on late payments. This n8n workflow checks your Google Sheets invoices every day at 9am, uses OpenAI to generate an overdue reminder with an escalating tone, and creates a Gmail draft for each client—then logs the chase in your sheet.

What this workflow does

• Runs on a schedule every day at 9am (Schedule Trigger).
• Reads invoice rows from the “Invoices” tab in Google Sheets.
• Filters for action: selects unpaid invoices that are past due and have not been chased in the last three days.
• Escalates reminder tone by assigning a reminder tier (e.g., polite, firmer, or final) based on how many days the invoice is overdue.
• Generates the email body with OpenAI using the invoice details and tier instructions.
• Creates Gmail drafts addressed to the client. For final notices, it appends the payment link from the sheet.
• Updates Google Sheets: sets “Last chased” to the current timestamp for the matched invoice row.

Use cases

• SaaS operations teams that invoice monthly and want consistent overdue follow-ups without daily manual effort.
• Freelancers/consultancies using Google Sheets as their billing source of truth and needing client-friendly reminders.
• n8n automation engineers who want an invoice chasing pattern combining Sheets tracking + OpenAI drafting + Gmail review.

Technical details

• Google Sheets: read from and update the Invoices tab (columns required include Invoice #, Client, Client email, Due, Amount, Status, Payment link, Last chased).
• Gmail: creates the reminder as a `draft` message to the client.
• OpenAI: drafts a short reminder email body with tier-appropriate tone.
• Schedule Trigger: runs daily at 9am; uses code logic to filter and assign tiers.
• Invoices marked Status = PAID are excluded.