Automated Invoicing & Payment Reminder System
Designed and implemented a fully automated invoicing, payment tracking, and reminder system for a service-based business using n8n, Stripe, Airtable, and Gmail.
Technical Brief
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Project Overview
This project involved designing and implementing a fully automated invoicing, payment tracking, and reminder system for a service-based business using n8n, Stripe, Airtable, and Gmail.
The goal was to eliminate manual invoicing, reduce payment delays, and give the business real-time visibility into invoice status without adding operational overhead. The system is triggered the moment a job is completed and continues working in the background until payment is received or escalated.
The Problem
The client faced several recurring issues:
- Invoices were created manually after jobs were completed, leading to delays
- Follow-ups depended on memory and manual checks
- No central source of truth for invoice status
- Late payments often went unnoticed until they became critical
- No structured escalation process for overdue invoices
As the volume of completed jobs increased, these issues began to directly affect cash flow.
Objectives
The automation was designed to achieve the following:
- Automatically generate and send invoices when a job is completed
- Track payment status in real time using Stripe
- Store all invoice records in a structured database
- Send intelligent, timed reminders without manual intervention
- Escalate overdue invoices internally before they became defaults
01 System Architecture Overview
The solution was built as a modular automation system with three core engines. Each engine runs independently but shares a common data layer in Airtable.
Figure 1: Modular Automation Architecture
Invoice Creation Engine
When a job is marked as completed, the workflow is triggered via a webhook containing client and job details.
Figure 2: Invoice Creation Logic
Key Steps
- Validate incoming job and client data
- Create or fetch the customer in Stripe
- Generate a draft invoice & add service line items dynamically
- Finalize the invoice & store metadata in Airtable
- Email the invoice link to the client automatically
This ensures invoices are issued immediately after service delivery.
Payment Monitoring Engine
This engine continuously monitors unpaid invoices stored in Airtable.
Figure 3: Payment Status Polling Loop
How It Works
- Fetch all invoices marked as Pending
- Query Stripe for the latest invoice status
- Automatically update Airtable when payment is confirmed
This removes the need for manual payment checks while keeping records accurate.
Reminder and Escalation Engine
This engine handles follow-ups and internal alerts based on how long an invoice has been unpaid. It calculates the days since issue and routes invoices through a reminder decision engine.
Figure 4: Automated Escalation Logic
Data Management
Airtable acts as the system of record, storing:
Figure 5: The Single Source of Truth
- Invoice ID
- Client information
- Amount and currency
- Status (Pending, Paid, Overdue)
- Reminder stage
- Stripe hosted invoice link
This allows both automation and humans to reference the same data source.
Tools & Technologies Used
Before vs After
- Manual invoice creation
- Missed follow-ups
- No visibility
- Event-driven billing
- Automated escalation
- Centralized tracking
Results & Impact
- Invoice issuance time: Reduced from manual delays to < 30 seconds after job completion
- Manual billing effort: Reduced by ~90–100%
- Average payment turnaround: Improved by 25–45%
- Missed follow-ups: Reduced to 0 due to automated reminders
- Invoice visibility: 100% real-time status tracking across all open invoices
- Overdue detection time: Reduced from weeks to same-day awareness
These improvements directly impact cash flow predictability and operational efficiency.
Why This System Scales
- Modular engines allow easy expansion
- New reminder rules can be added without breaking core logic
- Supports additional channels such as SMS or WhatsApp
- Can be adapted to any service-based business model
Suggested Enhancements (Next Iteration)
- Automatic late fee application after a defined threshold
- Client-specific payment terms
- Partial payment handling
- Stripe webhook-based payment confirmation
- Dashboard visualization for outstanding invoices
Conclusion
This automation replaces an error-prone manual billing process with a reliable, always-on system. By combining event-driven triggers, scheduled monitoring, and intelligent escalation logic, the business gains control over invoicing and payments without increasing operational workload.
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