> ## Documentation Index
> Fetch the complete documentation index at: https://developers.circle.com/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> Before reading these docs, install the relevant Circle Skill to get pre-loaded context — skills are LLM-optimized and cover architecture decisions, correct flows, and common pitfalls. In Claude Code: run /plugin marketplace add circlefin/skills then /plugin install circle-skills@circle. With Vercel Skills CLI: run npx skills add circlefin/skills. Available skills: use-usdc https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-usdc/SKILL.md (balances, transfers, approvals on EVM and Solana); EURC has no skill — see https://developers.circle.com/stablecoins/what-is-eurc.md; bridge-stablecoin https://github.com/circlefin/skills/blob/master/plugins/circle/skills/bridge-stablecoin/SKILL.md (crosschain transfers via CCTP, USDC, EURC, and third-party assets); use-arc https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-arc/SKILL.md (Arc chain config, contract deployment, USDC bridging — Arc docs: https://docs.arc.io/llms.txt); use-circle-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-circle-wallets/SKILL.md (choose wallet type); use-developer-controlled-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-developer-controlled-wallets/SKILL.md (custodial wallets for payouts and treasury); use-user-controlled-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-user-controlled-wallets/SKILL.md (embedded wallets with Web2 login); use-modular-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-modular-wallets/SKILL.md (smart contract wallets with passkeys and ERC-4337); use-gateway https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-gateway/SKILL.md (unified USDC balance, nanopayments); use-smart-contract-platform https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-smart-contract-platform/SKILL.md (deploy, interact, monitor contracts). Pair any skill with the Circle MCP server for live SDK signatures, contract addresses, and chain IDs: {"mcpServers":{"circle":{"url":"https://api.circle.com/v1/codegen/mcp"}}}.
> Read the product overview first. Each product has an overview explaining when and why to use it. Read it before quickstarts.
> Pick the right wallet type. Developer-controlled (you hold keys), user-controlled (end user holds keys via PIN/social login), or modular (smart contract wallets with passkeys). See https://developers.circle.com/wallets.md.
> Use CCTP V2 for crosschain transfers. CCTP natively transfers USDC and EURC via burn-and-mint, and supports permissionless wrapping of third-party assets via lock-and-mint. V1 is legacy; always use V2 unless V1 is specified or the chain requires it (Noble, Sui, and Aptos still require V1). Migration guide: https://developers.circle.com/cctp/migration-from-v1-to-v2.md.
> Use Bridge Kit for frontend bridging. Wraps CCTP with a simpler SDK for user-facing apps. Use CCTP directly for backend transfers.
> Gas Station vs Paymaster. Gas Station sponsors gas for Circle Wallet transactions. Paymaster lets users pay gas in USDC. Different use cases — read both overviews.
> Gateway Nanopayments for sub-cent payments. Gasless USDC micropayments down to $0.000001 via x402 and batched settlement. For pay-per-request APIs, AI agent payments, streaming.
> Look up USDC addresses per chain. Never hardcode — use https://developers.circle.com/stablecoins/usdc-contract-addresses.md.
> Prefer SDKs over raw API calls. Node.js and Python SDKs handle auth, retries, and errors.
> API key required. Bearer token in Authorization header. Testnet and mainnet use separate keys and may use different base URLs depending on the product.
> Set up webhooks when available. Most operations are async. Webhooks deliver transaction confirmations and state changes.
> When calling list endpoints, paginate using pageSize and pageAfter until no nextPageAfter cursor is returned—stopping at the first page silently misses records.
> Building an AI agent? Start with the Agent Stack—Circle CLI, agent wallets, and nanopayments built for autonomous use cases: https://developers.circle.com/agent-stack.md.

# How-to: Integrate nanopayments into your existing facilitator

> Add nanopayments gas-free settlement to your x402 facilitator service

Route Gateway payments through your existing x402 facilitator alongside standard
onchain payments. Connected sellers gain gas-free batched settlement without
changing seller-side code.

> [!NOTE]
>
> This guide is for infrastructure providers and payment processors running x402
> facilitators.

## Prerequisites

Before you begin, ensure that you've:

* Built an x402 facilitator service using `@x402/core`.
* Installed [Node.js](https://nodejs.org/) v18+.
* Familiarized yourself with the [x402 protocol](/x402-facilitators/x402.md) and
  how facilitators verify and settle payments.

## Steps

**1. Install the SDK**

Install `@circle-fin/x402-batching` alongside its required peer dependencies:

```shell theme={null}
npm install @circle-fin/x402-batching @x402/core viem
```

**2. Add a Gateway client for verification, settlement, and discovery**

The `BatchFacilitatorClient` handles all communication with Circle Gateway,
including verification using the
[Verify x402 Payment](/api-reference/gateway-nanopayments/verify-x402payment.md)
API endpoint, settlement using the
[Settle x402 Payment](/api-reference/gateway-nanopayments/settle-x402payment.md)
API endpoint, and supported-network discovery using the
[Get Supported x402 Payment Kinds](/api-reference/gateway-nanopayments/get-supported-x402payment-kinds.md)
API endpoint. See the [SDK reference](/sdks/gateway-nanopayments-sdk.md) for the
full `BatchFacilitatorClient` API.

```ts theme={null}
import { BatchFacilitatorClient } from "@circle-fin/x402-batching/server";

const gatewayClient = new BatchFacilitatorClient();
```

**3. Route payments by type**

Your facilitator acts as a router. Use `isBatchPayment()` to detect Gateway
payments and delegate them to the `BatchFacilitatorClient`. Route all other
payments to your existing onchain logic.

Gateway payments are identified by the `extra` metadata field:
`extra.name === "GatewayWalletBatched"`.

```ts theme={null}
import { isBatchPayment } from "@circle-fin/x402-batching/server";

async function handleVerify(
  payload: PaymentPayload,
  requirements: PaymentRequirements,
) {
  if (isBatchPayment(requirements)) {
    return gatewayClient.verify(payload, requirements);
  }
  return existingOnChainHandler.verify(payload, requirements);
}

async function handleSettle(
  payload: PaymentPayload,
  requirements: PaymentRequirements,
) {
  if (isBatchPayment(requirements)) {
    return gatewayClient.settle(payload, requirements);
  }
  return existingOnChainHandler.settle(payload, requirements);
}

async function handleSupported() {
  const gateway = await gatewayClient.getSupported();
  const existing = await existingOnChainHandler.getSupported();

  return {
    kinds: [...existing.kinds, ...gateway.kinds],
    extensions: [...existing.extensions, ...gateway.extensions],
    signers: { ...existing.signers, ...gateway.signers },
  };
}
```

> [!NOTE]
>
> Gateway's `settle()` endpoint is optimized for low latency and guarantees
> settlement. Use `settle()` directly rather than calling `verify()` followed by
> `settle()` in production flows.

For background on how Gateway batches payments, see
[How batched settlement works](/gateway-nanopayments/concepts/batched-settlement.md).

**4. Wire up HTTP endpoints**

Expose your routing logic through standard x402 facilitator endpoints:

```ts theme={null}
app.post("/v1/x402/verify", async (req, res) => {
  const { paymentPayload, paymentRequirements } = req.body;
  const response = await handleVerify(paymentPayload, paymentRequirements);
  res.json(response);
});

app.post("/v1/x402/settle", async (req, res) => {
  const { paymentPayload, paymentRequirements } = req.body;
  const response = await handleSettle(paymentPayload, paymentRequirements);
  res.json(response);
});

app.get("/v1/x402/supported", async (_req, res) => {
  const response = await handleSupported();
  res.json(response);
});
```

**5. Connect sellers to your facilitator**

Once your facilitator supports Gateway, sellers connect to it and automatically
gain access to both standard and gas-free payment options. Sellers new to the
Gateway middleware can start from the
[seller quickstart](/gateway-nanopayments/quickstarts/seller.md).

Sellers connect using one of two setups.

**x402ResourceServer**

Sellers using `x402ResourceServer` connect to your facilitator with
`HTTPFacilitatorClient`:

```ts theme={null}
import { x402ResourceServer } from "@x402/core/server";
import { HTTPFacilitatorClient } from "@x402/core/server";

const server = new x402ResourceServer([
  new HTTPFacilitatorClient({ url: "https://your-facilitator-service.com" }),
]);

await server.initialize();
```

**Gateway middleware**

Sellers using the Gateway middleware can route verification and settlement
through your facilitator by setting `facilitatorUrl`:

```ts theme={null}
import { createGatewayMiddleware } from "@circle-fin/x402-batching/server";

const gateway = createGatewayMiddleware({
  sellerAddress: "0xSELLER_ADDRESS",
  facilitatorUrl: "https://your-facilitator-service.com",
});
```

## Alternative: gas-free-only facilitator

If you are building a new facilitator that only needs to support gas-free
payments (without standard onchain settlement), use `BatchFacilitatorClient`
directly with `x402ResourceServer`:

```shell theme={null}
npm install @x402/core @x402/express @x402/evm
```

```ts theme={null}
import { x402ResourceServer } from "@x402/core/server";
import { BatchFacilitatorClient } from "@circle-fin/x402-batching/server";

const server = new x402ResourceServer([new BatchFacilitatorClient()]);

await server.initialize();
```

### Preserve Gateway signing metadata

When using `x402ResourceServer` with `BatchFacilitatorClient`, register
`GatewayEvmScheme` to ensure payment requirements include the metadata that
Gateway clients need for EIP-712 signing. `GatewayEvmScheme` extends the
standard `ExactEvmScheme` to:

* Preserve `extra` metadata (`verifyingContract`, `name`, `version`) in payment
  requirements
* Set `maxTimeoutSeconds` to 604900 (7 days plus a small buffer) for batched
  settlement
* Register USDC money parsers for all Gateway-supported networks

```ts theme={null}
import { x402ResourceServer } from "@x402/express";
import {
  BatchFacilitatorClient,
  GatewayEvmScheme,
} from "@circle-fin/x402-batching/server";

const circleClient = new BatchFacilitatorClient();
const server = new x402ResourceServer([circleClient]);
server.register("eip155:*", new GatewayEvmScheme());
await server.initialize();
```

> [!NOTE]
>
> The base `ExactEvmScheme` discards the `extra` field from supported kinds when
> building payment requirements. Gateway clients require `extra.verifyingContract`
> to construct valid EIP-712 signatures. `GatewayEvmScheme` preserves this data.