StablePay 2.0 - UPI to USDT Bridge

A decentralized application that enables users in India to pay merchants in INR via UPI, while merchants instantly receive USDT stablecoins in their wallet.

📁 Project Structure

StablePay2.0/
├── frontend/          # React + Vite frontend (Deploy to Vercel)
├── backend/          # Node.js + Express backend (Deploy to Render)
├── contarcts/        # Smart contracts (Deploy to Sepolia)
└── DEPLOYMENT.md     # Deployment guide

🚀 Quick Deploy

Want to deploy to production?

👉 QUICK-DEPLOYMENT-STEPS.md - Deploy in ~1 hour!

Need more info?

• Complete Deployment Guide
• Environment Variables
• Deployment Overview

🚀 Features

• Seamless UPI to USDT Bridge: Users pay in INR, merchants receive USDT
• MetaMask Integration: Connect wallet and execute transactions on Sepolia testnet
• KYC Verification: Phone verification and document upload for compliance
• Smart Contract Integration: Uses FiatUSDTSwap contract for secure swaps
• Real-time Conversion: Live INR to USDT rates with GST calculation
• Transaction History: View all swap transactions and balances
• Responsive Design: Works on desktop and mobile devices

🛠 Tech Stack

Frontend:

• React + Vite
• TypeScript
• Tailwind CSS
• ethers.js v6
• React Router DOM

Backend:

• Node.js + Express
• Supabase (Database & Storage)
• Real-time subscriptions

Blockchain:

• Ethereum Sepolia Testnet
• Custom FiatUSDTSwap Smart Contract
• ERC20 USDT Token

📋 Prerequisites

Before running the application, you need:

1. MetaMask Extension installed in your browser
2. Sepolia ETH for gas fees (get from Sepolia Faucet)
3. Contract Addresses - Deploy contracts first (see contarcts/ folder)

🔧 Development Setup

Frontend Setup

cd frontend
npm install
npm run dev

See frontend/README.md for details.

Backend Setup

cd backend
npm install
npm run dev

See backend/README.md for details.

Smart Contracts

cd contarcts
npm install
npx hardhat run scripts/deploy.js --network sepolia

See contarcts/README.md for details.

🌐 Deployment

Quick Deployment Guide

1. Deploy Backend to Render

   • See backend/RENDER-DEPLOYMENT.md
   • Get your backend URL (e.g., https://stablepay-backend.onrender.com)

2. Deploy Frontend to Vercel

   • See frontend/README.md
   • Set VITE_API_URL to your backend URL

3. Update Backend CORS

   • Add frontend Vercel URL to ALLOWED_ORIGINS
   • Restart backend service

For complete deployment instructions, see DEPLOYMENT.md.

📚 Documentation

• Frontend: frontend/README.md - Frontend setup and Vercel deployment
• Backend: backend/RENDER-DEPLOYMENT.md - Backend setup and Render deployment
• Contracts: contarcts/README.md - Smart contract deployment
• Deployment: DEPLOYMENT.md - Complete deployment guide

🔧 Setup Instructions

1. Clone and Install

   git clone <repository-url>
   cd StablePay2.0
   npm install

2. Configure Environment

   • Click "Connect to Supabase" in the top right of the application
   • This will set up your database tables automatically

3. Update Contract Addresses

   • Deploy your FiatUSDTSwap contract to Sepolia
   • Update the contract addresses in src/utils/blockchain.ts

4. Start Development Server

   npm run dev

📱 How to Use

For Users (Sending Payments):

1. Connect Wallet: Click "Connect Wallet" and approve MetaMask connection
2. Verify Phone: Complete phone verification (uses demo OTP system)
3. Enter Amount: Input INR amount to convert to USDT
4. KYC Check: For amounts >$200, complete KYC verification
5. Execute Swap: Confirm transaction in MetaMask (ensure you're on Sepolia)

For Merchants (Receiving Payments):

1. Connect Wallet: Connect your MetaMask wallet
2. View Dashboard: See your USDT balance and transaction history
3. Monitor Transactions: Real-time updates of incoming swaps

🔐 Smart Contract Functions

The application integrates with these key contract functions:

• calculateSwap(): Get conversion rates and GST amounts
• swapUSDTToFiat(): Execute USDT to fiat currency swaps
• getUserSwapHistory(): Retrieve user's transaction history
• getRecentSwaps(): Get recent platform transactions

🌐 Network Configuration

The app automatically switches to Sepolia testnet. Network details:

• Chain ID: 11155111 (0xaa36a7)
• RPC URL: Sepolia Infura endpoint
• Block Explorer: https://sepolia.etherscan.io

🔍 Transaction Flow

1. User enters INR amount
2. Smart contract calculates USDT equivalent + GST
3. User approves USDT spending (if needed)
4. Contract executes swap and records transaction
5. Event emitted and UI updated with transaction hash

🛡 Security Features

• KYC Compliance: Phone verification and document upload
• Transaction Limits: $200 threshold for enhanced verification
• Smart Contract Security: Uses OpenZeppelin's SafeERC20
• Network Validation: Ensures transactions on correct network

📊 Database Schema

The app uses Supabase with these main tables:

• users: User profiles and KYC status
• transactions: Transaction records with amounts and status
• kyc_documents: Uploaded verification documents
• otp_storage: Phone verification codes

🚀 Deployment

The application is deployed and accessible at: [Your Deployment URL]

To deploy your own instance:

1. Deploy smart contracts to Sepolia
2. Update contract addresses in the code
3. Configure Supabase project
4. Deploy frontend to your preferred hosting platform

🤝 Contributing

1. Fork the repository
2. Create a feature branch
3. Make your changes
4. Test thoroughly on Sepolia testnet
5. Submit a pull request

📄 License

This project is licensed under the MIT License.

⚠️ Disclaimer

This is a demo application for educational purposes. Do not use with real funds on mainnet without proper security audits and regulatory compliance.