For decades, HTTP 402 Payment Required has been reserved for future use. x402 unlocks it, and .
is a standard, but rarely used, HTTP response status code indicating that payment is required to access a resource.
In x402, this status code is activated to:
Inform clients (buyers or agents) that payment is required.
Communicate the details of the payment, such as amount, currency, and destination address.
Provide the information necessary to complete the payment programmatically.
The primary purpose of HTTP 402 is to enable frictionless, API-native payments for accessing web resources, especially for:
Machine-to-machine (M2M) payments (e.g., AI agents).
Pay-per-use models such as API calls or paywalled content.
Micropayments without account creation or traditional payment rails.
Using the 402 status code keeps x402 protocol natively web-compatible and easy to integrate into any HTTP-based service.
HTTP 402 is the foundation of the x402 protocol, enabling services to declare payment requirements directly within HTTP responses. It:
Signals payment is required
Communicates necessary payment details
Integrates seamlessly with standard HTTP workflows