Sippy

Sippy is a WhatsApp-based wallet that enables anyone with a phone number to send and receive PYUSD without installing apps, managing seed phrases, or understanding blockchain. Users simply text "send 5 to +573001234567" and money moves instantly on Arbitrum.

The Problem: Traditional cross-border payments are slow and expensive. Crypto promises better, but wallets, gas fees, and seed phrases prevent mainstream adoption.

Our Solution: Every phone number automatically gets a secure Coinbase CDP wallet. Users never see private keys or gas fees—they just text naturally in English or Spanish, and money moves.

Key Features:

• Natural language commands ("cuánto tengo?" works like "check balance")
• Gasless experience via smart contract coverage
• Cross-chain onboarding from many networks using Avail Nexus SDK
• Zero friction: no downloads, no KYC, no seed phrases
• Blockscout-powered transaction explorer for transparency

Market: 650 million people in Latin America where 90% use WhatsApp. Colombia's Bre-B and Brazil's Pix prove phone-based payments work, but none cross borders. Sippy fills that gap.

Backend (Node.js + TypeScript):

• Coinbase CDP SDK v2: MPC wallets in Trusted Execution Environment. Phone numbers map to CDP accounts with no seed phrases. This is simpler account abstraction than traditional AA solutions: phone numbers become the abstraction layer without ERC-4337 complexity.
• WhatsApp Cloud API: Webhook-based bot with hybrid parsing (natural language + regex fallback = 100% uptime). Limited to 5 test numbers until Meta approval for production.
• PostgreSQL (Railway): Stores phone to wallet mappings and spending limits.

Frontend (Next.js 15):

• Avail Nexus SDK: Cross-chain bridging from any supported chain to Arbitrum. Uniswap Universal Router: Multi-hop swap ETH to WETH to USDC to PYUSD with slippage protection.
• Blockscout API v2: Real-time balances and transaction history. Smart Contract:

Blockchain (Harhat)

• GasRefuel.sol on Arbitrum: Auto-refuels users when ETH < 0.00001, with daily limits and cooldowns.

Notable Challenges:

• PYUSD Routing: Nexus doesn't support PYUSD natively, so we bridge ETH then swap via Uniswap Universal Router: Reverse-engineered command encoding (0x0b00 = WRAP_ETH + V3_SWAP_EXACT_IN)
• CDP v2: No high-level token transfer method. Manually constructed ERC-20 callData: selector + ABI-encoded parameters
• WhatsApp Test Environment: Limited to 5 test numbers before Meta approval, requires manual addition for demo

Note: Some security practices and production optimizations were intentionally left for post-hackathon due to time constraints. Many improvements are planned for UX, data management, rate limiting, authentication, and privacy controls before public launch.