x402 Payments (Set-and-Forget)

The x402 protocol (an extension of the HTTP 402 Payment Required status) allows APIs to monetize individual endpoints by demanding a microtransaction before returning a resource. While x402 is powerful for agent-to-agent (A2A) commerce, existing implementations have two critical gaps:

The wallet popup — every time an agent hits a paywall, the human user must manually confirm a transaction.
Invisible to agents — endpoints using the official @x402 packages don’t appear in any agent directory until a human manually registers them.

@delegare/x402 solves both. It combines x402 with Intent Mandates for set-and-forget payments, and simultaneously emits discovery headers that make your endpoint automatically appear on Delegare Market (which aggregates across protocols), agentic.market (CDP Bazaar), and mppscan.com.

How It Works

Agent requests data

The agent calls POST /api/extract on the merchant’s server.

Merchant returns 402 challenge

The middleware responds with 402 Payment Required containing three parallel discovery payloads:

PAYMENT-REQUIRED header (base64 JSON) — x402 v2, read by CDP Bazaar and @x402/fetch clients
WWW-Authenticate: Payment ... header — MPP/RFC 7235, read by MPPScan and MPP-compatible wallets
JSON body — x402 v1, backward-compatible with older clients

SDK auto-pays via Delegare

@delegare/sdk intercepts the 402, verifies the amount is within the agent’s budget, and forwards the intent mandate to Delegare’s settlement infrastructure.

Settlement on Base

Delegare settles on Base L2 via the mandate’s session key and the DelegareRouter contract. USDC arrives directly in the merchant’s wallet. No popups.

Agent receives data

The agent retries with a payment credential. The middleware verifies it and returns the gated resource.

CDP Bazaar indexes the endpoint

On the first settlement via the CDP Facilitator (PAYMENT-SIGNATURE credential), CDP writes a catalog entry. The endpoint appears on agentic.market within ~10 minutes.

For Merchants: Monetizing APIs

Basic setup

npm install @delegare/x402

import express from 'express';
import { requireX402Payment } from '@delegare/x402';

const app = express();

app.get('/premium-data',
  requireX402Payment({
    price: '0.05',
    payTo: '0xYourMerchantWalletAddress',
  }),
  (req, res) => {
    res.json({ secret: 'AI agents love this data' });
  }
);

Adding agent discovery

Use declareDiscoveryExtension before requireX402Payment to make your endpoint searchable on Delegare Market, agentic.market, and mppscan.com:

import { requireX402Payment, declareDiscoveryExtension } from '@delegare/x402';

app.post('/api/extract',
  declareDiscoveryExtension({
    description: "Extract structured financial data from documents. $0.15/page.",
    inputSchema: {
      type: "object",
      properties: {
        documentId: { type: "string" },
        domain: { type: "string", enum: ["commercial_loan", "equity_investment"] }
      },
      required: ["documentId"]
    },
    bodyType: "json",
    output: {
      example: { extractedData: { gross_income: 1250000 }, costCents: 150 },
      // schema is required — output.example alone is not enough for Bazaar
      schema: {
        type: "object",
        properties: {
          extractedData: { type: "object" },
          costCents: { type: "number" }
        }
      }
    }
  }),
  requireX402Payment({ price: '0.15', payTo: '0xYourWallet' }),
  async (req, res) => { res.json({ data: '...' }); }
);

What the middleware handles

Client credential	Rail	What happens
None	—	Returns `402` with x402 v2, MPP, and v1 discovery payloads
`X-Bundle-Token`	Fiat credit bundle	Validates JWT, deducts credit from your DB
`PAYMENT-SIGNATURE`	x402 v2 USDC	Settles via CDP Facilitator → indexes on agentic.market
`X-PAYMENT`	x402 v1 USDC	Settles via Delegare Facilitator
`X-DELEGARE-MANDATE`	AP2 intent mandate	Settles via Delegare Vault using session key
`Authorization: Payment`	MPP/RFC 7235	Settles via Delegare Facilitator

You never touch private keys or on-chain logic. USDC arrives directly in your wallet from the Base blockchain.

Required env vars for Bazaar indexing

COINBASE_API_KEY=your-cdp-key-id       # CDP API key UUID
COINBASE_API_SECRET=your-base64-secret  # Base64-encoded Ed25519 key (64 bytes)

When set, the middleware authenticates CDP settlement calls — required for the catalog write to succeed on first settlement.

Configuration reference

requireX402Payment({
  price: '0.05',                    // Decimal USDC
  payTo: '0xYourWallet',            // Base wallet address
  testMode: true,                   // Use Base Sepolia (default: false)
  apiUrl: 'https://api.sandbox.delegare.dev/v1',
  resource: 'https://yourapi.com/api/endpoint', // Full URL — used as catalog key
  mimeType: 'application/json',
  maxTimeoutSeconds: 300,
  creditBundle: { ... }
});

Accessing payment context

app.get('/premium-data',
  requireX402Payment({ price: '0.05', payTo: '0xYourWallet' }),
  (req, res) => {
    const payer = (req as any).x402Payer;        // Payer's wallet address
    const txHash = (req as any).x402Transaction;  // On-chain tx hash
    res.json({ data: '...', paidBy: payer });
  }
);

Read the x402 Middleware Documentation for the full configuration reference and fiat bundle setup.

For Agents: Seamlessly Paying Paywalls

Replace standard fetch calls with delegare.fetch. When the API returns a 402, the SDK resolves it automatically using the user’s intent mandate.

import { Delegare } from '@delegare/sdk';

const delegare = new Delegare({ merchantId: '...', apiKey: '...' });

// If the API returns a 402, the SDK auto-pays and retries — no popups.
const response = await delegare.fetch(
  'https://merchant.com/premium-data',
  { method: 'GET' },
  userIntentMandate
);

How the SDK resolves x402

Makes the initial request.
On 402, sends the intent mandate via X-DELEGARE-MANDATE.
Merchant middleware forwards to Delegare for settlement.
Delegare settles on-chain via the mandate’s KMS-encrypted session key.
SDK returns the final response with the gated data.

The agent never holds private keys. The session key is scoped to the individual mandate — not accessible to the agent, merchant, or Delegare.

x402 v2 clients (`@x402/fetch`)

Agents using Coinbase’s @x402/fetch client send a PAYMENT-SIGNATURE credential. The middleware routes this to the CDP Facilitator, which also triggers Bazaar indexing on first settlement.

Model Context Protocol (MCP)

If your agent runs on MCP (Claude, ChatGPT, or any MCP-compatible client), the delegare_fetch tool handles x402 automatically:

"Fetch the data from https://merchant.com/premium-data using my mandate"

No code required — the MCP server resolves the 402 challenge behind the scenes.

Discovery: How Agents Find Your API

declareDiscoveryExtension embeds metadata in every 402 response. Three directories index it:

Platform	Protocol	Header read	How to appear
market.delegare.dev	x402 v2 + MPP	Both	Auto-aggregated from the two below
agentic.market	x402 v2	`PAYMENT-REQUIRED`	Auto on first CDP Facilitator settlement
mppscan.com	MPP/RFC 7235	`WWW-Authenticate`	Register at mppscan.com/register

Delegare Market is the primary destination — it aggregates x402 and MPP endpoints from both upstream sources. Agents using the Delegare SDK or searching via Claude/ChatGPT tools query it in one request. All three read inputSchema and outputSchema from the metadata to show agents what parameters your endpoint accepts and what it returns.

Documentation Index

​How It Works

​For Merchants: Monetizing APIs

​Basic setup

​Adding agent discovery

​What the middleware handles

​Required env vars for Bazaar indexing

​Configuration reference

​Accessing payment context

​For Agents: Seamlessly Paying Paywalls

​How the SDK resolves x402

​x402 v2 clients (@x402/fetch)

​Model Context Protocol (MCP)

​Discovery: How Agents Find Your API

How It Works

For Merchants: Monetizing APIs

Basic setup

Adding agent discovery

What the middleware handles

Required env vars for Bazaar indexing

Configuration reference

Accessing payment context

For Agents: Seamlessly Paying Paywalls

How the SDK resolves x402

x402 v2 clients (`@x402/fetch`)

Model Context Protocol (MCP)

Discovery: How Agents Find Your API