PaidUp - Invoice Reminder SaaS

Demo mode: reminder emails are logged instead of sent, the Pro upgrade is simulated, and the demo data resets daily.

PaidUp is a complete, working SaaS that chases unpaid invoices automatically for freelancers and small agencies. Users add an invoice, pick a reminder schedule, and PaidUp sends a polite nudge before the due date, a friendly reminder on the day, and a firm follow-up when it is overdue, until the invoice is marked paid.

This is real, production-ready source code, not a UI mockup: authentication, database, subscription billing and the scheduled email system are all implemented. Every row is protected by Postgres Row Level Security, and plan limits are enforced in the database, not just in the UI.

Built with Next.js 16 (App Router), React 19, TypeScript, Tailwind CSS 4, Supabase (Auth + Postgres), Stripe Checkout and Resend. Deploys to Vercel in minutes, with the daily reminder job included as a Vercel Cron.

Features

• Invoices with a 3-stage reminder schedule: before, on, and after the due date
• Automatic daily reminder emails via Resend; idempotent, so retries never double-send
• Editable email templates with merge tags: {{client_name}}, {{amount}}, {{invoice_number}}, {{due_date}}
• Dashboard with open, paid and canceled invoices and the next scheduled reminders
• One-click "Mark paid" stops all further reminders
• Free plan (3 active invoices) and Pro plan via Stripe Checkout
• Signature-verified Stripe webhook upgrades and downgrades the plan
• Supabase Auth (email + password) with Row Level Security on every table
• Plan and free-tier limits enforced in the database
• Responsive layout from phone to desktop
• Optional demo mode for running your own public demo
• Unit tests (Vitest) for money, scheduling and template logic
• Step-by-step setup guide (DOCUMENTATION.md)
• Customization guide: change the name, logo, colors and landing text (exact files listed)

Requirements

• Node.js 20 or newer and npm
• A Supabase account (free tier is enough)
• A Stripe account (for the Pro subscription)
• A Resend account (for sending reminder emails)
• A Vercel account recommended for hosting and the daily cron job

Instructions

1. Extract the archive and run: npm install
2. Create a Supabase project and run the SQL files in supabase/migrations in order (0001, 0002, 0003) in the SQL Editor.
3. In Stripe, create a monthly subscription price and a webhook endpoint for /api/stripe/webhook with the events checkout.session.completed and customer.subscription.deleted.
4. Create a Resend account and a sending domain or address.
5. Copy .env.local.example to .env.local and fill in your Supabase, Stripe, Resend and cron keys.
6. Run: npm run dev, then open http://localhost:3000
7. To go live, import the project into Vercel, add the same environment variables and deploy. vercel.json schedules the daily reminder job.

Full details are in DOCUMENTATION.md inside the archive.