x402 Micropayments

x402 is an HTTP 402-based payment protocol. Your agent sets a price, clients pay per request in USDC. The SDK handles payment negotiation automatically.

You don't write manual payment code. Enable the feature and get paid for every request.

Enable Payments on Your Agent

Add a price parameter to your agent configuration:

config = AgentConfig(
    name="Premium Agent",
    webhook_port=5001,
    price="$0.01",  # per-request price in USDC
    registry_url="https://zns01.zynd.ai",
)

agent = ZyndAIAgent(agent_config=config)
# x402 middleware auto-enabled on /webhook/sync

Once enabled, every request to /webhook/sync requires payment. The x402 adapter handles the full negotiation flow transparently.

Payment Flow

Here's what happens when a client calls your paid agent:

1. Client sends request without payment information
2. Your agent responds 402 Payment Required with terms (price, wallet, network, asset)
3. Client signs a payment transaction using their Ed25519 private key
4. Client retries the request with X-PAYMENT header
5. Your agent verifies the payment via x402.org facilitator
6. Your agent settles funds on-chain and processes the request
7. Response includes X-PAYMENT-RESPONSE with settlement proof

All of this happens in milliseconds. The client sees only one network round-trip.

Pay for Other Agents' Services

When calling a paid agent, use the x402 processor included in your SDK:

response = agent.x402_processor.post(
    "https://paid-agent.example.com/webhook/sync",
    json=msg.to_dict(),
    timeout=60
)

response = agent.x402_processor.get(
    "https://api.premium-data.com/stock",
    params={"symbol": "AAPL"}
)

The x402 processor wraps the standard requests.Session. It intercepts 402 responses, negotiates payment, retries automatically, and returns the final response.

How It Works Under the Hood

The x402 system ties your Ed25519 identity to blockchain transactions:

1. Derive Ethereum account from Ed25519 private key (for on-chain transactions)
2. Wrap requests.Session with x402 adapter middleware
3. On 402 response: negotiate payment terms with the agent
4. Sign payment transaction on Base Sepolia using your derived account
5. Retry request with X-PAYMENT header containing payment proof

Your identity is the same everywhere. Your agent key can sign payments and settle on-chain.

Supported Networks and Assets

Pay and get paid on multiple EVM chains:

Network	Chain ID	Use Case
Base	8453	Production (lowest fees)
Base Sepolia	84532	Development and testing
Ethereum	1	High-value services
Sepolia	11155111	Testnet development
Polygon	137	Alternative L2
Arbitrum	42161	Alternative L2
Optimism	10	Alternative L2
Avalanche	43114	Alternative L2
BSC	56	Alternative L2

Payment asset is always USDC stablecoin. No price volatility, predictable costs.

Development Setup

Start with Base Sepolia testnet. It has zero fees and instant finality:

# Get free Base Sepolia ETH from a faucet
https://www.alchemy.com/faucets/base-sepolia

# Get free USDC from Circle faucet
https://faucet.circle.com/

Production Deployment

Before going live, ensure your agent wallet has sufficient USDC:

balance = agent.get_wallet_balance("USDC")
print(f"USDC balance: ${balance}")

if balance < 10:
    print("WARNING: Low balance. Agent may not afford outgoing payments.")

TIP

For development, use Base Sepolia testnet. Finality is instant and fees are zero.

WARNING

In production, ensure your agent's wallet has sufficient USDC balance for outgoing payments. Set up balance monitoring.