Build Multi-Tenant UPI AutoPay Mandate + Payment Link + Dynamic QR Platform

We are looking for an experienced FinTech/Payment Integration Developer to build a secure and scalable UPI payment platform with the following core modules: 1. UPI AutoPay Mandate * UPI AutoPay mandate creation/registration * Mandate authorization flow * Mandate status enquiry * Mandate cancellation/revocation * Mandate lifecycle management * Recurring/debit transaction processing * Pre-debit workflow where applicable * Failed/Pending transaction handling * PSP/Bank API integration * Webhook/callback processing The integration will be based on APIs/documentation provided by our approved PSP/Bank/Payment Partner. ### 2. UPI Payment Link * Generate unique payment links through API/Admin Panel * Fixed and configurable payment amount * Order/Customer reference * Link expiry * Payment status tracking * Success/Failure/Pending handling * Mobile-friendly payment page * UPI app/deep-link support where applicable * Webhook notification after payment Example flow: Merchant → Create Payment Link → Customer Opens Link → UPI Payment → PSP/Bank → Webhook → Transaction Status Updated ### 3. Dynamic UPI QR Generator * Generate dynamic UPI QR codes * Unique QR for each transaction/order * Amount and transaction reference * QR expiry where applicable * PNG/SVG QR output * Payment status tracking * API-based QR generation * QR transaction history ### 4. Multi-Tenant/Merchant System The platform should be designed for multiple merchants/tenants. Required: * Tenant/Merchant management * Merchant-wise API credentials/API keys * Merchant-wise transactions * Merchant webhook URL/configuration * Secure tenant data isolation * Merchant transaction reports ### 5. Backend & APIs We require REST APIs for: * Mandate creation * Mandate status * Mandate cancellation * Payment link creation * Payment status * QR generation * Transaction status enquiry * Webhook/callback handling * Merchant/tenant management Swagger/OpenAPI documentation and Postman Collection must be provided. ### 6. Transaction & Webhook Management The system must properly handle: CREATED → INITIATED → PENDING → SUCCESS / FAILED Requirements: * Idempotency * Duplicate webhook protection * Webhook signature verification * API timeout handling * Transaction status reconciliation * Webhook retry mechanism * Complete transaction/audit logs Payment success should never depend only on frontend/browser redirects. Final payment status must be verified through server-side PSP/Bank APIs or authenticated callbacks. ### 7. Admin Dashboard A basic admin dashboard is required for: * Merchants/Tenants * Mandates * Payment Links * QR Payments * Transactions * Success/Failed/Pending transactions * Webhook logs * Search by Order ID / Transaction ID / Mandate ID * Basic transaction reports ### Preferred Technology Backend: * Node.js + TypeScript OR Java Spring Boot Database: * PostgreSQL Preferred: * Redis * Queue/Background Workers * Docker * React/Next.js Admin Panel We are open to alternative technology recommendations if properly justified. ### Security Requirements This is a FinTech/payment project, therefore security and code quality are very important. Developer must implement: * Secure API authentication * API key management * Role-based access where required * Rate limiting * Input validation * Idempotency * Secure webhook verification * Sensitive data masking * Secure credential/secret management * Audit logging * No hard-coded production credentials ### Deliverables Developer must provide: * 100% project source code * Backend APIs * Admin dashboard * Database schema & migrations * PSP/Bank integration * Swagger/OpenAPI documentation * Postman Collection * Deployment/setup documentation * `.env.example` * Docker configuration where applicable * Testing and bug fixes * Production deployment assistance All source code and intellectual property developed specifically for this project must be handed over to us upon completion. ### Developer Requirements Please apply only if you have previous experience with FinTech, payment gateway, UPI, recurring payments, mandates, or similar payment API integrations. When applying, please answer: 1. Have you previously integrated UPI or payment gateway APIs? 2. Have you worked specifically with UPI AutoPay/Mandates? 3. Which PSP/Bank/Payment Gateway APIs have you worked with? 4. How will you prevent duplicate transactions/webhooks? 5. How will you handle PENDING transactions and API timeouts? 6. What technology stack do you recommend? 7. Estimated development timeline? 8. Fixed project cost? 9. How much post-deployment support will you provide? Please do not submit generic proposals. We are specifically looking for a developer with strong backend, payment API, webhook, transaction lifecycle, and security experience.