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The x402 protocol turns the long-dormant HTTP 402 Payment Required status code into a live, machine-readable payment handshake. Instead of issuing API keys, managing subscription tiers, or building billing dashboards, you embed a sub-cent USDC price directly into your HTTP response — and the client pays before the request is served. Settlement happens on-chain on Arc testnet (chain ID: 5042002) via Circle Nanopayments, with no manual reconciliation on your end.

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Why x402?

Traditional API monetization forces you to build auth systems, handle failed payments, and chase down overdue invoices. x402 eliminates that entirely:
  • Zero onboarding friction — AI agents and developer tools that speak x402 can call your API without signing up for an account or entering credit card details.
  • Automatic settlement — each request triggers an on-chain Circle Nanopayment; USDC lands in your wallet without batch payouts or manual withdrawals.
  • Sub-cent granularity — charge $0.001 or even $0.0005 per call, enabling monetization models that subscriptions can never support.
  • Agent-native — autonomous AI agents using ERC-8004 on-chain identities can discover, pay for, and consume your API end-to-end without human intervention.

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How the Protocol Works

Every x402 interaction follows the same five-step flow regardless of whether you self-host middleware or publish on the FlareHQ Marketplace:
1

Client requests your endpoint

A developer tool or AI agent sends a normal HTTP request to your API — no special headers yet.
2

FlareHQ returns HTTP 402

Your endpoint (or the FlareHQ proxy) responds with HTTP 402 Payment Required and a JSON body that contains the price in USDC, the payTo wallet address, and the Arc testnet chainId.
3

Client signs a Circle Nanopayment authorization

The client — either a FlareHQ SDK call or a compatible x402 library — signs an EIP-712 structured payload authorizing a Circle Nanopayment for the exact amount and destination specified in the 402 response.
4

FlareHQ verifies the proof and settles on-chain

FlareHQ validates the cryptographic payment proof, executes sub-cent on-chain settlement on Arc testnet, and credits the seller’s gateway balance.
5

Request is proxied; response returned to client

Once payment is confirmed, the original request is forwarded to your upstream API. The response — your actual data payload — is returned to the client with a 200 OK.

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Two Integration Paths

You can add x402 monetization to your API in two ways. Choose the one that fits your infrastructure:

Self-hosted middleware

Install the FlareHQ middleware on your own Express or Next.js API. You keep full control of the server and upstream logic; the middleware intercepts requests, validates payment proofs, and lets verified requests through.

x402 Marketplace

Publish a listing on the FlareHQ Marketplace with your upstream URL. FlareHQ handles the proxy, payment verification, and settlement entirely — your server only receives pre-verified, already-paid requests.
Both paths use the same underlying x402 protocol and Circle Nanopayments settlement. The middleware gives you more control; the Marketplace gives you discoverability and zero-infrastructure overhead.

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Next Steps

Paywall Setup

Add an x402 paywall to your own API endpoint using the FlareHQ Express or Next.js middleware.

x402 Marketplace

Publish your API as a discoverable listing and let FlareHQ handle proxying and settlement.

Agent Payments

Learn how autonomous AI agents authenticate with ERC-8004 and pay for API access automatically.