Automate Overdue Invoice Emails with Google Sheets & n8n

Automatically escalate overdue invoices from Google Sheets—every day

This n8n workflow checks your Google Sheets invoices daily, calculates how many days each pending invoice is overdue, sends the correct Spanish escalation email via SMTP, and then updates the sheet with the latest notice level and date.

What this workflow does

• Runs on a schedule: it executes every day at 09:00 (Europe/Madrid) using an n8n Schedule Trigger.
• Reads invoice rows from Google Sheets: it pulls invoice records from the configured spreadsheet (documentId and sheetName in both read and update steps).
• Filters and calculates overdue days: it focuses on invoices where estado="pendiente", optionally skips weekends, and computes days overdue from vencimiento.
• Chooses an escalation level: it selects escalation thresholds at 7 / 21 / 45 days overdue, but only if the escalation hasn’t been sent yet.
• Sends a Spanish email escalation: it generates an email subject and body using templates for the selected level (including configurable company name and signature).
• Sends via SMTP: it delivers the email to the invoice contact using SMTP credentials and the configured fromEmail.
• Updates Google Sheets after sending: it matches invoices by numero and writes the latest nivel_aviso and ultimo_aviso date to the corresponding row.

Use cases

• Reduce manual follow-ups by escalating unpaid invoices to customers automatically after 7/21/45 days.
• Keep your accounts receivable process consistent across your team using a single Google Sheets source of truth.
• Operate a lightweight SaaS billing reminder system without building a full custom portal.

Technical details

• Integrations/Nodes: Schedule Trigger, Google Sheets (read + update), Code (calculation + template selection), Email send (SMTP), and supporting steps used in the workflow logic.
• Required sheet columns: numero, cliente, email, importe, vencimiento, estado, nivel_aviso, ultimo_aviso.
• Configuration: Google OAuth2 credentials for reading/updating; SMTP credential with correct domain fromEmail; adjustable thresholds, weekend skipping, and Spanish email templates.