Problem Statement :

Currently in countries like India, the cryptocurrency adoption is very low. You cannot but any products/services with crypto, so we are stuck with centralised fiat, But that's going to change now. [Note: P2P crypto to fiat exchanges in India is a mess - it took me an hour last time to get the crypto for the hackathon staking.]

Solution

FullOnCrypto solves this problem by delegating the fiat INR payment to others(resolvers) and settle them in DAI(crypto) + fee in eth(crypto).

BASE MAINET CONTRACT:

PaymentEscrow contract: 0x7e7E2bBB58C1F7C710005797C48705747877C647

BASE TESTNET CONTRACT:

PaymentEscrow contract: 0x0C446A3e9c245E255D7d9cE994cd5321BA4E52A4

1-Inch APIs used:

1. Balances API - To fetch he current users token balances to be displayed in the profile page.
2. Token API - To fetch the token metadata to display the logo of the token. Used both common tokens API and specific token API for DAI.
3. Spot Price API - To fetch the INR price of the token.
4. Gas price API - To show the current GAS proce of the BASE chain to the users and resolvers.

🏗️ Architecture

This monorepo contains three main applications:

📱 Frontend (fulloncrypto-web/)

• Tech Stack: React, TypeScript, ethers.js
• Purpose: User interface for creating and managing crypto payment requests
• Features:
  • QR code scanning for UPI payments
  • MetaMask wallet integration
  • Payment request management
  • Real-time crypto balances
  • Gas price monitoring
  • resolver features for commiting and settlement of UPI payment

🔗 Backend API (fulloncrypto-nodejs/)

• Tech Stack: Node.js, Express, MongoDB
• Purpose: Backend API for user management and payment data
• Features:
  • User authentication (traditional & wallet-based)
  • Payment request storage and indexing
  • UPI ID mapping for smart contracts, storing paymentCriticalData off-chain in MongoDB
  • CORS-enabled API endpoints

📜 Smart Contracts (fulloncrypto-contract/)

• Tech Stack: Solidity, Hardhat, OpenZeppelin
• Purpose: Escrow contracts on Base blockchain
• Features:
  • Payment escrow with DAI deposits
  • Commitment-based payment flow
  • Automatic crypto release upon UPI confirmation
  • Gas-optimized for Base network

Blockers faced during hackathon:

1. [HIGH] [Mocked] - Verifying the the UPI transactionId status on-chain using oracle. But i need to have a PaymentGateway lisence to get access to the transactionStatus API, So it is mocked with a regex for now.
2. [HIGH] [Fixed] - Generating a UPI QR code on behalf of a merchant, here when creating a payment request you want the upi QR to have the destination UPI-address of the merchant. Currently no paymentGateway provides this functionality but i solved it using barebones mobile upi deep-link. eg: upi://pay?pa=<UPI_ID>&pn=<NAME>&am=<AMOUNT>&cu=INR&tn=<NOTE>
3. [HIGH] [Fixed] - Merchant UPI address is a payment-critical-data and cannot be stored in public blockchain, so i used mongoDB off-chain storage.
4. [HIGH] [FIXED] - Double payment by resolvers was a concern, so i introduced a 5-min commitment window. First a resolver should commit to a payment on blockchain by paying gas and the settke it in 5-mins.

Note: For building this project, I've used assistance of AI to fine-tune the code and the UI styles and documentation