Full-Stack Developer for Secure Voucher Verification

We need a senior full-stack developer to build a mini pilot for a secure voucher verification and redemption platform. We already have a designed website and a private GitHub repository. The developer will build the backend, admin dashboard, database, OTP flow, status tracking, reports, and deployment setup. Pilot scope: - 500 to 1,000 test vouchers - Web-based redemption flow - Admin dashboard - PostgreSQL database - Secure voucher code generation - Hashed voucher code storage - OTP verification flow - Mock payment/status provider first - Webhook/status update endpoint - CSV export for voucher batch - CSV export for redemption report - Basic fraud controls - Deployment on VPS - Setup and handover documentation Required features: 1. Admin can create a campaign. 2. Admin can generate voucher batches. 3. System stores voucher codes securely. 4. Users can enter a voucher code. 5. System checks if the voucher is valid, active, unused, and unexpired. 6. User verifies phone number with OTP. 7. System records redemption status. 8. Admin can view active, used, pending, failed, and blocked vouchers. 9. Admin can search by serial number or phone number. 10. Admin can export reports. Important: - We own the repository and all source code. - No hardcoded secrets. - Use environment variables. - No live financial integration is required in phase one. - Build mock provider structure first. - Code must be clean, documented, and ready for later integration. Please reply with: 1. Your proposed tech stack. 2. Similar backend/API projects. 3. How you will prevent duplicate voucher use. 4. How you will secure voucher codes. 5. Timeline. 6. Fixed price.