Micro-Investing App with Dhan Integration

I’m building a secure, zero-custody micro-investing platform for Blobiz Solutions and need an experienced full-stack developer who has already shipped FinTech products that talk to broker APIs.

The very first user journey I want live is daily savings through UPI AutoPay, automatic payment collection, and the resulting NIFTYBEES purchase. After each day’s successful payments are tallied, the app should fire one consolidated buy order via the DhanHQ API. To make that possible, users will connect their brokerage by signing directly into Dhan through a secure OAuth-style flow—no manual key entry or admin intervention.

Core scope
• Deep DhanHQ API integration for order placement, portfolio pull, and trade status callbacks.
• UPI AutoPay setup to collect ₹50/₹100 daily as well as monthly subscription fees, with fallback to a standard UPI gateway for one-offs.
• Affiliate rewards pool: maintain a virtual cashback ledger that nudges users to link their Demat so earned rewards can be auto-invested.
• Real-time and scheduled messaging: WhatsApp alerts, Firebase push notifications, SMS OTP, and daily reconciliation summaries.
• Backend on PostgreSQL (Supabase or AWS Lambda preferred) with cron jobs for payment reconciliation and one-per-day order placement logic.
• Admin web panel for user KYC status, payment logs, brokerage linkage health, and override controls.

Technical expectations
React Native or Flutter on the front end, Node.js/TypeScript or Go for backend lambdas, strong command over secure key management, and experience with payment webhooks and broker rate limiting.

Deliverables
1. Production-ready mobile apps (Android & iOS) and web admin panel.
2. Fully documented source code in a GitHub repo transferred to us.
3. Postman collection or Swagger docs for every internal endpoint.
4. Deployment scripts (CI/CD) and brief hand-over session.

If your portfolio already shows broker API integrations, especially in Indian markets, let’s talk. Please outline your high-level approach, estimated timeline, and a ballpark cost along with any clarifying questions.