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.