Django SaaS Billing & Inventory

I’m putting together a cross-platform billing and inventory SaaS that must run smoothly on the web (React) and mobile (Flutter). The core stack is already chosen: a Django backend with a PostgreSQL database, all deployed on AWS.

Key functional blocks you’ll build and wire up:

• Subscription engine – monthly recurring plans driven by Razorpay Subscriptions API, with optional Stripe fallback, automatic invoicing, proration, and dunning logic.
• GST-compliant invoice management – create, edit, email, and share invoices; integrate with the GSTN e-invoicing APIs for real-time IRN and QR code generation.
• Inventory & batch tracking – receive stock, monitor quantities, lot/expiry dates, and link sales orders to inventory reductions.
• Offline-first data layer – the mobile app must work without connectivity and sync seamlessly when a connection returns, resolving conflicts gracefully.
• Role-based security – Admin, staff, and accountant levels with encrypted data at rest and in transit.
• Reports & analytics – sales, taxes, inventory valuation, MRR, and churn visualisations downloadable as PDF/CSV.
• Bilingual UI – instant Tamil/English toggle across web and mobile.

Acceptance snapshot
1. React web app and Flutter mobile app compile without warnings, pass unit tests, and connect to the same Django REST API.
2. All payment, GSTN, and cloud calls succeed in a staging account before production cut-over.
3. Stock, invoicing, and subscriptions reconcile in reports for at least 1,000 concurrent users in load tests.
4. Switching a device to airplane mode, creating invoices, then reconnecting shows correct sync on every client.

If you’ve handled similar fintech or GST-integrated projects on Django/PostgreSQL and AWS, let’s talk about your proposed timeline and milestone plan.