Charge for an API

Protect a fixed-price API route with the x402 exact scheme on Base.

Charge a known amount before returning an API response. In the Base USDC flow used here, x402 carries an EIP-3009 authorization through the HTTP 402 Payment Required handshake, then a facilitator verifies and settles it.

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Demo

The demo above is mock only. If you want to see onchain demos on Vibenet, head to Base chain demos.

These examples target Base Sepolia (eip155:84532) and the public x402.org test facilitator. To take a route live, see Move to Base Mainnet.

1. Return Payment Requirements

   The unpaid request receives a 402 response with the scheme, network, token, price, and recipient.
2. Sign and Retry

   The buyer applies its spend policy, signs the advertised payment, and retries with PAYMENT-SIGNATURE.
3. Verify Before Work

   Seller middleware verifies the payload before your protected handler runs.
4. Settle

   The facilitator submits the payment and returns settlement details with the response.

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Price a Fixed Route

TypeScript · Express

app.use(paymentMiddleware({
  "GET /fixed": {
    accepts: [{ scheme: "exact", price: "$0.01", network, payTo }],
    description: "Fixed-price market report",
    mimeType: "application/json",
  },
}, resourceServer));
app.get("/fixed", (_request, response) => response.json({ report: "Base market summary" }));

An unpaid request receives 402; a valid paid retry reaches the handler and returns the resource once.

Treat the facilitator response and your own fulfillment record as separate checks. Make the route idempotent so a retried paid request cannot deliver the same one-time resource twice.

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Move to Base Mainnet

The public x402.org facilitator supports testnets only. Before you take a route live on Base mainnet:

1. Choose a production facilitator path: a hosted facilitator that supports Base mainnet, such as the CDP Facilitator, your own facilitator, or self-facilitation inside your resource server. The x402 docs list other production facilitators.
2. Set network to Base mainnet (eip155:8453) and payTo to a mainnet address you control.
3. Confirm the asset. A dollar price such as "$0.01" on Base resolves to USDC (0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913), which settles through EIP-3009 transferWithAuthorization on the USDC contract. Other ERC-20 tokens settle through Permit2.
4. Call your facilitator’s supported endpoint and check that it lists eip155:8453 with the scheme your route uses.

The CDP Facilitator supports Base mainnet with the exact, upto, and batch-settlement schemes, screens payments against OFAC and KYT checks, and authenticates with a CDP API key. See Network and token support for other networks and assets.

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See Also

Settle Usage-Based Payments

Set the final charge after successful work.

Call a Paid Service

Add network, asset, and spend policy on the buyer.