The Future is Now: Real-time, Pay-per-Use Payments with X402

Written by: By Eray ALTILI, CYBER SECURITY ARCHITECT,  Proven leader for global orgs like World Bank, NATO, and UN.

X402 An open protocol for internet-native payments

x402 is an open payment protocol developed by Coinbase that enables instant, automated stablecoin payments directly over HTTP. It is designed to allow web services, APIs, and AI agents to transact autonomously, unlocking real-time, pay-per-use monetization for digital resources, APIs, and content. x402 leverages the long-reserved HTTP status code 402 Payment Required to natively support payments as part of the web protocol, using stablecoins like USDC and operating across multiple blockchains.

How x402 Works

x402 introduces a payment handshake between clients (such as AI agents, apps, or browsers) and resource servers (APIs, web services) using standard HTTP requests and responses, augmented with custom headers and payloads:

1. Client Requests Resource

• The client (e.g., an AI agent or app) requests access to a protected resource (API endpoint, dataset, premium content).

2. Server Responds with 402 Payment Required

• If payment is needed, the server returns an HTTP 402 Payment Required status, including a JSON payload specifying:

• Amount required (e.g., $0.01)
• Supported token (e.g., USDC)
• Blockchain network (e.g., Base, Solana)
• Recipient wallet address
• Expiry, nonce, and other metadata.

3. Client Submits Payment

• The client constructs a payment payload, signs it with its wallet (EIP-712 standard), and resends the original request with the payment proof in the X-PAYMENT HTTP header.

4. Payment Verification

• A facilitator service (such as Coinbase’s x402 Facilitator) or the server itself verifies the payment on-chain, checking for validity, correct amount, and preventing replay attacks.

5. Resource Delivered

• Upon successful verification, the server responds with the requested data (HTTP 200 OK) and includes an X-PAYMENT-RESPONSE header confirming the transaction

Example x402 Payment Flow

1. Client: GET /premium-data 2. Server: 402 Payment Required   {     “maxAmountRequired”: “0.01”,     “assetType”: “ERC20”,     “assetAddress”: “0xA0b86991c6218b36c1d19d4a2e9eb0ce3606eb48”, // USDC     “paymentAddress”: “0x1234…abcd”,     “network”: “base-mainnet”,     “expiresAt”: “2025-07-03T20:00:00Z”,     “nonce”: “abcd1234”,     “paymentId”: “xyz789”   } 3. Client: GET /premium-data   X-PAYMENT: (base64-encoded JSON with payment proof, signed by wallet) 4. Server: 200 OK   X-PAYMENT-RESPONSE: (base64-encoded receipt)   (Resource data in body)

x402 Components

Component	Role	Key Features
Client	Initiates payment, signs payloads, retries reqs	EIP-712 signing, wallet integration, automated payments
Resource Server	Enforces payment, sets pricing, serves content	HTTP 402 responses, pricing tables, middleware
Facilitator	Verifies payment on-chain, prevents replay	Signature verification, nonce tracking, gas abstraction
Blockchain	Settles payments, ensures immutability	Stablecoin transfers (USDC), smart contracts

Why x402 Matters

• Native to HTTP: Uses standard HTTP flows and headers, no plugins or third-party payment processors required.
• Pay-per-use & Micropayments: Enables charging as little as $0.001 per API call or data query, unlocking new business models.
• Automation: Designed for AI agents and microservices to transact autonomously, without human intervention or API keys.
• Chain-agnostic & Fast: Works with multiple blockchains (starting with Base), with finality in seconds and very low fees.
• Open Standard: Not locked to Coinbase; anyone can implement facilitators or integrate the protocol.

Example Use Cases

• Paid APIs: Monetize endpoints on a per-call basis, e.g., $0.01 per request for premium data.
• AI Agents: Allow autonomous agents to pay for compute, data, or services as needed.
• SaaS Features: Unlock on-demand SaaS features with real-time, per-use billing.
• Content Monetization: Charge for access to articles, datasets, or digital downloads without subscriptions.

Technical Example: Payment Payload

The payment payload, sent in the X-PAYMENT header, is a base64-encoded JSON object, for example:

{  “x402Version”: 1,  “scheme”: “exact”,  “resource”: “/premium-data”,  “maxAmountRequired”: “0.01”,  “payTo”: “0x1234…abcd”,  “asset”: “0xA0b86991c6218b36c1d19d4a2e9eb0ce3606eb48”,  “nonce”: “abcd1234”,  “signature”: “0x…” }

In summary: x402 is a protocol that brings native, automated, stablecoin payments to the web via HTTP, enabling machine-to-machine commerce, API monetization, and frictionless pay-per-use access for both humans and AI agents.

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Eray ALTILI, CYBER SECURITY ARCHITECT, Proven leader for global orgs like World Bank, NATO, and UN.