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x402 Overview

x402 is an open protocol for HTTP-native payments. It uses the HTTP 402 Payment Required status code to enable machine-readable payment negotiation directly in the request/response cycle — no API keys, no subscriptions, no out-of-band billing.

OMATrust integrates with x402 in two ways: as a reputation layer for x402-enabled services, and through the Offer and Receipt extension which produces cryptographic proof-of-interaction for attestations.

x402 resourceUrl as Service Identity​

Every x402 payment flow is anchored to a resourceUrl — the URL of the paid endpoint. This URL maps directly to a did:web identifier:

resourceUrl: https://api.example.com/premium-data
         →  did:web:api.example.com

This means any x402-enabled service automatically has an identity that can serve as the subject of OMATrust attestations — the same way an app store listing identifies a service for reviews and ratings. No additional registration step is needed to start building reputation for a paid endpoint.

Why x402 Matters for OMATrust​

The internet has no standard way for a service to say "pay me" and for a client to respond with payment — all in a single HTTP exchange. x402 solves this at the protocol level: a server returns 402 with machine-readable payment terms, the client pays, and the server delivers the resource.

This creates a natural integration point for OMATrust:

  • Signed offers prove that a server committed to specific payment terms. These can be used as evidence in attestations even if no payment occurs.
  • Signed receipts prove that a client paid and received service. These serve as cryptographic proof-of-interaction for User Review attestations — the equivalent of a "Verified Purchase" badge.
  • Both artifacts are portable — they can be lifted out of the x402 flow and submitted to OMATrust's EAS-based reputation layer as proof objects attached to attestations.

How It Works​

┌─────────┐                      ┌─────────────────┐
│  Client  │                      │ Resource Server  │
└────┬─────┘                      └────────┬─────────┘
     │                                     │
     │  GET /resource                      │
     │ ───────────────────────────────────►│
     │                                     │
     │  402 + Payment Terms                │
     │     + Signed Offer(s)               │
     │ ◄───────────────────────────────────│
     │                                     │
     │  GET /resource + Payment Header     │
     │ ───────────────────────────────────►│
     │                                     │
     │  200 + Resource                     │
     │     + Signed Receipt                │
     │ ◄───────────────────────────────────│
     │                                     │
     │  ┌──────────────────────┐           │
     │  │ Submit receipt as    │           │
     │  │ proof in OMATrust    │           │
     │  │ User Review          │           │
     │  └──────────────────────┘           │
  1. Client requests a paid resource
  2. Server responds with 402 including payment requirements and signed offers
  3. Client signs a payment authorization and re-requests with the signed authorization in the header
  4. Server verifies payment, delivers the resource, and returns a signed receipt
  5. Client can later attach the receipt to an OMATrust User Review attestation as proof of interaction

Integration Guides​

Further Reading​