Send multi-stage overdue invoice reminders with NocoDB, Gmail and PostGrid

What Is This? This workflow is an automated invoice payment tracking and vindication system that monitors unpaid and overdue invoices stored in NocoDB, then sends escalating reminders to clients based on configurable time thresholds. The system handles three escalation levels: friendly payment reminders before/at due date, formal warning notices for overdue invoices, and legal action notifications for severely overdue accounts. It works with any accounting system that can populate a NocoDB database, making it ideal for businesses using custom invoicing systems, international accounting software, or multiple invoice sources. Who Is It For? Designed for small to medium-sized businesses, IT service providers, consulting agencies, and accounting departments that need professional payment enforcement without expensive debt collection services. This workflow is particularly valuable for companies experiencing cash flow challenges due to late-paying clients. B2B service providers, software development agencies, consultancies, and freelancers managing multiple client invoices will benefit from automated, multi-channel payment reminders that maintain professional relationships while firmly enforcing payment terms. Whether you're tracking 5 high-value contracts or managing 200+ monthly invoices, this automation ensures no payment deadline slips through the cracks. It's especially useful for businesses operating internationally or using accounting systems without built-in reminder features. How Does It Work? This comprehensive invoice vindication automation consists of four main stages: 1. Configuration & Company Details Setup Defines critical parameters including escalation timeframes (Days before Due Date for reminder, Days after Due Date for warning, Days after Due Date for Legal action), and toggles for notification channels (Send Email, Send Physical Letter). The workflow also captures complete company information for professional correspondence including banking details, tax identification numbers, and contact information. !image.png(fileId:5153) 2. Invoice & Client Data Retrieval Connects to NocoDB to fetch all invoices with their associated client information. The workflow uses a Split in Batches node to process each invoice individually, retrieving complete client details (name, email, full address) from the linked Clients table. This two-step fetch ensures all necessary data is available for personalized communications. !image.png(fileId:5151) 3. Intelligent Filtering & Categorization Invoices are filtered to remove already-paid invoices (checking both Invoice Status ≠ "Paid" and Payment Date = empty), then categorized into three escalation groups: - Today/Upcoming Invoices: Due date is today OR X days away → Sends friendly payment reminder - Overdue for Warning: Exactly Y days past due date → Sends formal warning about potential legal action - Overdue for Legal Notice: Exactly Z days past due date → Sends notice of commenced legal proceedings !image.png(fileId:5152) 4. Multi-Channel Notification Dispatch For each escalation level, the workflow generates professionally formatted HTML content with complete invoice details, payment instructions, and appropriate urgency levels. Notifications are dispatched via: - Email (Gmail): Professional HTML emails with company branding - Physical Mail (PostGrid): Printed letters delivered via postal service for serious escalations - Slack: Internal team notifications for tracking sent reminders !image.png(fileId:5150) Each notification includes invoice number, amounts, due dates, payment details (bank account, SWIFT code), and clear call-to-action based on escalation level. !image.png(fileId:5154) How To Set It Up? Prerequisites: - An active N8N account or self-hosted instance - A NocoDB instance (hosted at your domain or using NocoDB Cloud) - A Slack workspace with bot permissions - (Optional) Gmail account configured for sending emails - (Optional) PostGrid account for physical mail deliver