ScanGo

Problem Statement

This is your new digital payment gateway, built to bring you the ultimate convenience through a simple QR code system. When you're ready to buy something, just scan the code with your phone, and you’re done! We designed it to integrate stablecoins (like USDC or USDT) so you can pay using a value that is protected and steady—no more worrying about market ups and downs. ScanGo takes care of all the tricky conversions in the background, making sure the store instantly gets paid in their local money. This means faster transactions for you, no need to carry cash or cards, and a smarter way to handle your money using stable digital assets

Solution

Gasless stablecoin payment system using Fisher/Relayer pattern in TypeScript + Node.js. Fisher manages payment queue with EIP-191 validation, Relayer executes ERC20 transactions on Sepolia using ethers.js v6. EVVM integration (@evvm/testnet-contracts) for virtual blockchain, Express REST API, QR payments with deep links, automatic gas sponsorship that calculates costs and sponsors transactions. 5 RPC fallbacks for 99% uptime, real-time stats, MATE token support. The hacky part: EVVM's async nonces allow out-of-order transactions, crucial for high volume. Users experience instant gasless payments while maintaining Ethereum security.