PLUTO — Agentic Payment Infrastructure on Stellar

PLUTO is a dual-mode payment infrastructure built on Stellar that bridges the gap between traditional Web3 e-commerce (human-driven checkouts via Freighter) and the emerging headless machine economy (AI agents interacting autonomously via the x402 Payment Required protocol).

As AI agents become more capable and autonomous, they need a native way to pay for API access, computational resources, and premium data without human intervention. PLUTO provides a robust framework that enables developers and merchants to seamlessly monetize API endpoints for AI agents natively on the Stellar blockchain.

How it works (x402 Protocol)

import { x402Middleware } from './middleware/x402.js';

app.get('/api/my-paid-endpoint',
  x402Middleware({ amount: '0.10', recipient: 'G...YOUR_ADDRESS' }),
  (req, res) => res.json({ data: 'you paid for this' })
);

Replay attack prevention

Every verified tx_hash is stored in the x402_payments table. Reusing a transaction hash returns 409 Conflict.

Access tokens

Short-lived JWTs (60s expiry) signed with X402_JWT_SECRET. Agents include them as X-Payment-Token header on retries.

---

Stellar Testnet Interaction

This project makes real Stellar testnet transactions:

• Payment creation stores recipient Stellar addresses
• Horizon polling confirms on-chain USDC/XLM payments
• x402 agent submits real USDC payments on testnet
• All transactions verifiable on Stellar Expert (testnet)

USDC issuer (testnet): GBBD47IF6LWK7P7MDEVSCWR7DPUWV3NY3DTQEVFL4NAT4AQH3ZLLFLA5

---

Quick Start

Prerequisites

• Node.js 18+
• Redis
• Supabase account
• Stellar testnet wallet (Freighter)

Backend

cd backend
cp .env.example .env
# Fill in SUPABASE_URL, SUPABASE_SERVICE_ROLE_KEY, DATABASE_URL
npm install
npm run migrate
npm run dev

Frontend

cd frontend
cp .env.example .env.local
# Set NEXT_PUBLIC_API_URL=http://localhost:4000
npm install
npm run dev

Run the x402 agent demo

cd backend
node scripts/demoAgent.js

---

Environment Variables

# Supabase
SUPABASE_URL=
SUPABASE_SERVICE_ROLE_KEY=
DATABASE_URL=

# Stellar
STELLAR_NETWORK=testnet
STELLAR_HORIZON_URL=https://horizon-testnet.stellar.org
USDC_ISSUER=GBBD47IF6LWK7P7MDEVSCWR7DPUWV3NY3DTQEVFL4NAT4AQH3ZLLFLA5

# x402
X402_JWT_SECRET=your_secret_here
X402_TOKEN_EXPIRY_SECONDS=60
X402_PROVIDER_PUBLIC_KEY=G...YOUR_PROVIDER_ADDRESS

# Redis
REDIS_URL=redis://localhost:6379

---

What's Next

• MPP (Stripe Machine Payments) — payment channels for high-frequency agent interactions without per-tx fees
• Agent marketplace — merchants list paywalled APIs, agents discover and pay autonomously
• Ethereum support — same frontend, separate backend service for ERC-20 payments
• Spending policies — contract accounts with per-agent USDC limits

---

Hackathon Notes & Judging Criteria

Real Stellar Testnet Interaction

• All Stellar interactions use actual testnet transactions (we do not mock blockchain actions).
• Payment creation stores dedicated Stellar recipient addresses per merchant.
• Our Horizon polling engine confirms on-chain USDC/XLM payments in real-time.
• The x402 agent script submits actual USDC micropayments on the testnet.
• All transactions are entirely verifiable on Stellar Expert (testnet).

Unfinished Features & Mock Data (Requirement 1 Disclosure)

While the core payment processing and x402 logic is 100% functional, the following areas contain placeholders or are unfinished due to hackathon time constraints:

1. Analytics Dashboard: The merchant volume chart on the frontend dashboard currently displays synthesized local data curves for visual demonstration; the real-time aggregation pipeline from Supabase is not fully implemented.
2. Settings Persistence: Some deep settings (like custom coloring options for the checkout UI) store temporarily in state but aren't fully wired to apply dynamic CSS globally.
3. Machine Payment Protocol (MPP): Our planned Stripe-like payment channels for high-frequency agent actions (to avoid per-txn standard fees) was architected but not finished in this version.
4. Ethereum Support: Our backend architecture allows for ERC-20 payment routing, but we have exclusively rolled out Stellar indexing for this MVP.

• Open Source: The full source code is public in this repository.
• The dual video focus: PLUTO bridges the visual e-commerce gap (1-page Freighter checkouts) seamlessly alongside headless Machine economies (x402 agent payments). Both run off the exact same resilient backend.