Pay402

Pay402: First x402 Payment Facilitator on SUI

We're bringing proven technology to SUI with unique advantages impossible on other blockchains.

Market Context: x402 is Production-Ready

x402 (HTTP 402 "Payment Required") is a proven protocol for micropayments:

• $600M annualized payment volume (Dec 2025)
• 63M+ monthly transactions
• 1,100+ projects using the protocol
• Live on Base (Coinbase SDK) and Solana (PayAI)

The opportunity: SUI has NO x402 facilitator yet. We're first.

The Problem with Current Implementations

Existing x402 on Base and Solana face limitations:

• High friction: Users need wallet extensions, seed phrases, crypto knowledge
• Gas complexity: Users must hold gas tokens (ETH, SOL) in addition to USDC
• Slow finality: 12+ minutes on Ethereum L1, ~2 seconds on Base L2
• Expensive receipts: $0.50-$5 per on-chain event on EVM makes micropayments uneconomical

Our Solution: SUI's Unique Capabilities

Pay402 leverages SUI-native features to deliver the best x402 implementation, period:

1. Onboarding Non-Crypto Users (zkLogin + Enoki) → Google OAuth creates blockchain address. No wallet, no seed phrase, no crypto knowledge.

2. No Browser Wallet (Gas Sponsorship - Native) → Facilitator pays all SUI gas fees. Users only need USDC.

3. Low Latency (Sub-Second Finality) → 600-700ms blockchain settlement on testnet. Real-time payment confirmation.

4. Audit & Conflict Resolution (Cheap On-Chain Events) → Receipt events cost ~$0.0003 per payment (vs $0.50-$5 on EVM). Makes micropayments viable.

5. Flexible Extensions (Programmable Transaction Blocks) → Atomic multi-step: split coins, pay merchant, pay facilitator, emit receipt - all in one transaction.

6. Massive Scaling (Object Model - Owned Objects) → Parallel execution without shared state bottlenecks. Fundamentally different from EVM.

These capabilities are difficult or impossible on EVM/Solana chains.

Live Demo

URL: https://merchant-production-0255.up.railway.app (SUI Testnet)

Try it now: 1️⃣ Visit merchant → Click "Get Premium Data ($0.10)"
2️⃣ Sign in with Google (no wallet needed!)
3️⃣ Get test USDC from faucet (first time only)
4️⃣ Review payment (widget verifies transaction)
5️⃣ Confirm with 1-click (zkLogin signature)
6️⃣ Content delivered instantly
7️⃣ Receipt on blockchain

Proof Transaction: https://suiscan.xyz/testnet/tx/EV7D7z9gjzjrAQSKWSW8S1iLGdk8aEVPjn3zLA1aUSLE

Real payment on SUI testnet showing: buyer zkLogin signature, facilitator gas sponsorship, atomic USDC transfers, on-chain receipt.

Hackathon Achievements

Built during ETH Global HackMoney 2026:

✅ OAuth Login (zkLogin + Enoki)
✅ Gas Sponsorship (native SUI)
✅ PTB Validation (client-side security)
✅ zkLogin Signing (1-click payments)
✅ Optimistic Settlement (instant delivery)
✅ Pessimistic Settlement (wait for finality)
✅ USDC Persistence (Circle native)
✅ Merchant Onboarding (JWT invoices)
✅ On-Chain Receipts (cheap audit trail)

Testing: 276 automated tests passing
Deployment: Live on Railway (facilitator + widget + merchant)

Why This Matters

For SUI Ecosystem: First x402 brings proven payment infrastructure ($600M ecosystem) to SUI, enabling:

• API monetization for SUI developers
• Content paywalls with zero user friction
• AI agent commerce on SUI
• New revenue models for dApps

For x402 Protocol: Demonstrates that SUI's unique features (zkLogin, PTBs, object model) enable the BEST x402 implementation - superior to EVM and Solana.

Technical Innovation: Shows how SUI-native features eliminate complexity that requires workarounds on other chains (EIP-4337 for gas abstraction, smart contract wallets for social recovery, etc.)

Technical Implementation

GitHub Repository: https://github.com/hamiha70/Pay402

Full Documentation:

• A - Mermaid diagrams, payment flows
• T - Security analysis, PTB verification
• P - Market context, comparisons
• M - On-chain logic

Technology Stack

On-Chain (SUI Blockchain):

• Smart Contract: SUI Move with generic Coin<T> support
• PTBs: Programmable Transaction Blocks for atomic execution
• zkLogin: Zero-knowledge proofs for OAuth-based signing
• Gas Sponsorship: Native SUI feature (no EIP-4337 complexity)
• Event Emission: Cheap on-chain receipts (~$0.0003)
• Stablecoin: Circle USDC (native on SUI)

Off-Chain Components:

Facilitator API (Node.js + TypeScript):

• PTB construction matching invoice terms
• Balance verification
• Dual settlement modes (optimistic/pessimistic)
• Gas sponsorship coordination

Payment Widget (React + Vite):

• zkLogin integration (Enoki SDK)
• Client-side PTB verification (security critical)
• Stripe-like payment UX
• OAuth session management

Demo Merchant (Node.js + Express):

• JWT invoice generation
• HTTP 402 response pattern
• Payment verification
• Content delivery

Infrastructure:

• Enoki SDK (Mysten) - zkLogin infrastructure
• Railway - Deployment platform
• SUI Testnet - Network
• 276 automated tests - Coverage

Example Transaction: https://suiscan.xyz/testnet/tx/EV7D7z9gjzjrAQSKWSW8S1iLGdk8aEVPjn3zLA1aUSLE

SUI-Specific Advantages That Enable This

1. zkLogin + Enoki (Unique to SUI)

Google OAuth creates a deterministic SUI address via zero-knowledge proofs. No browser extension, no seed phrase required.

2. Programmable Transaction Blocks (SUI Native)

Atomic multi-step transactions: split coins, transfer to merchant, transfer facilitator fee, emit receipt - all succeed or all revert together.

3. Object Model with Parallel Execution

Owned objects enable parallel transaction processing without global state locks. Multiple payments execute simultaneously without coordination overhead.

4. Native Gas Sponsorship

ptb.setGasOwner(facilitatorAddress) - built into the protocol. Buyer signs with USDC, facilitator signs with SUI, neither can spend the other's funds.

Why better than Solana: Solana supports it but less elegantly. SUI's implementation is cleaner and native.

What Stands out

Technical Depth:

• Full-stack implementation (Move, TypeScript, React)
• Novel use of SUI-native features (zkLogin, PTBs, gas sponsorship)
• Production-quality security (PTB verification, JWT auth)
• Comprehensive testing (276 tests)

Real-World Utility:

• Solves actual problem (proven by $600M x402 market)
• Live demo anyone can try
• Clear path to mainnet deployment

SUI Ecosystem Contribution:

• First x402 on SUI - brings proven protocol to network
• Demonstrates SUI advantages over EVM/Solana
• Example of excellent SUI developer UX
• Enables new revenue models for SUI dApps

Next Steps / Roadmap

Immediate (Post-Hackathon):

• Mainnet deployment
• Production monitoring (Sentry, uptime tracking)
• Multi-region facilitator nodes

Short-Term:

• Browser extension for PTB verification (works with any x402, not just Pay402)
• Embeddable widget (npm package)
• Merchant SDK for easy integration

Medium-Term:

• CCTP integration (Circle's Cross-Chain Transfer Protocol) - merchants receive on preferred chain
• Support for additional stablecoins beyond USDC
• Merchant dashboard for reconciliation

Partner Technologies

Mysten (SUI):

• SUI blockchain and Move language
• Enoki SDK for zkLogin
• Native gas sponsorship, PTBs, object model

Circle:

• USDC stablecoin (native on SUI)
• Future: CCTP for cross-chain settlement

Railway:

• Infrastructure for deploying all services
• Simple GitHub integration

Solo Hacker Context

Every aspect of this project - smart contract design, Move implementation, facilitator API architecture, widget UI/UX, PTB verification algorithm, testing strategy, documentation, and presentation - was built by one person during the hackathon.

The comprehensive scope demonstrates:

1. SUI's excellent documentation and developer resources
2. Move's safety and expressiveness for payment logic
3. Enoki SDK's production-readiness for zkLogin
4. The power of SUI-native features to eliminate complexity