L402 is a standard for authenticating and paying for internet services, including application programming interface endpoints and computational resources. Its documented payment flow revives the HTTP 402 Payment Required status code, unused for years, and returns a Lightning invoice to the client requesting access.

Payment becomes part of the request

In the documented L402 flow, a client asks for a protected resource and the service responds with HTTP 402 Payment Required plus a Lightning invoice. The client pays that invoice, receives proof linked to the payment, and uses the proof to authenticate a new request for the resource.

This combines authentication and payment in the service request instead of treating billing as a separate account process. The standard is built for internet services such as application programming interface endpoints and computational resources, where software may need to pay before it can continue a task.

The HTTP 402 code has existed as Payment Required for years, but it has long lacked a common payment flow. L402 gives that status code a specific process built on Lightning: the service issues the requirement and invoice, and the client then returns authorization linked to that payment when it asks for access again.

Resources for a vision of agentic commerce

The project describes a possibility, still some way off, in which software pays other software for services. It presents that vision of agentic commerce as a vision rather than a guaranteed result, while documenting the L402 flow used for payment and authentication.

The L402 project presents agentic commerce as a vision for the long run, one in which software can pay software for services. That is still just a vision. The documented standard does address one concrete prerequisite, though: it gives software a shared flow for authentication and payment over Lightning.

Application programming interface access and computational resources are the clearest examples in the documentation. A client that understands L402 can run into a payment requirement, pay the attached Lightning invoice, and present the proof linked to that payment to get access to the service.

Why It Matters

L402 places a Lightning invoice inside the documented access flow for application programming interfaces and computational resources. That gives software a standard route from request to payment to authentication. It is a concrete building block for the project's vision of agentic commerce, which is still some way off. Software cannot buy services on its own without a way to read a price and act on it. Bitcoin provides the monetary asset, Lightning supplies fast settlement, and L402 connects that settlement to service access. If agentic commerce develops, an open Bitcoin payment standard offers a stronger base than another platform balance controlled by a single intermediary.