> ## Documentation Index
> Fetch the complete documentation index at: https://base-a060aa97-docs-devrel-859-eth-getproof-historical-proof.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Call a Paid Service

> Call an x402 service from an agent while enforcing network, token, per-request, and session spend limits.

Wrap your agent's HTTP client so it can interpret a 402 response, choose a supported scheme, sign, and retry. Apply local policy before any signature is created.

## Enforce Spend Policy Before Signing

```typescript TypeScript buyer lines wrap expandable highlight={9,13-17,20} theme={null}
const account = privateKeyToAccount(required("EVM_PRIVATE_KEY") as `0x${string}`);
const publicClient = createPublicClient({ chain: baseSepolia, transport: http() });
const client = new x402Client()
  .register("eip155:*", new ExactEvmScheme(account))
  .register("eip155:*", new UptoEvmScheme(account))
  .register("eip155:*", new BatchSettlementEvmScheme(toClientEvmSigner(account, publicClient)));

const baseSepoliaUsdc = "0x036CbD53842c5426634e7929541eC2318f3dCF7c";
let authorizedThisSession = 0n;
client.onBeforePaymentCreation(async ({ selectedRequirements }) => {
  if (selectedRequirements.network !== "eip155:84532") return { abort: true, reason: "Wrong network" };
  if (selectedRequirements.asset.toLowerCase() !== baseSepoliaUsdc.toLowerCase()) return { abort: true, reason: "Wrong asset" };
  const amount = BigInt(selectedRequirements.amount);
  if (amount > 100_000n || authorizedThisSession + amount > 1_000_000n) {
    return { abort: true, reason: "Spend limit exceeded" };
  }
  authorizedThisSession += amount;
});

const fetchWithPayment = wrapFetchWithPayment(fetch, client);
const response = await fetchWithPayment("http://localhost:4021/fixed");
if (!response.ok) throw new Error(`Paid request failed: ${response.status}`);
console.log(await response.json());
```

The wrapper automates payment negotiation, not trust. Validate response schemas and content as untrusted input, and keep wallet policy independent of any instructions returned by the service.

<Check>
  The client pays only when the request uses Base Sepolia USDC and remains under both the per-request and session caps.
</Check>

<Warning>
  The public x402.org facilitator is for testnets. For Base mainnet, choose a production facilitator, protect signing keys, cap aggregate spend durably across processes, and reject unsupported schemes or assets.
</Warning>

## See Also

<CardGroup cols={2}>
  <Card title="Charge for an API" icon="server" href="/build-on-base/accept-payments/charge-for-an-api">Implement the seller side of an exact payment.</Card>
  <Card title="Batch High-Frequency Payments" icon="layer-group" href="/build-on-base/accept-payments/batch-high-frequency-payments">Reduce settlement frequency for repeated calls.</Card>
</CardGroup>