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

# Pay-per-call Setup

> Make your first pay-per-call request in TypeScript or Python.

## Prerequisites

* A wallet on any of 11 supported EVM chains (Ethereum, Base, Arbitrum, Optimism, etc.)
* USDC deposited via [Circle Gateway](https://www.circle.com/gateway)
* `x402-fetch` (Node) or `x402-requests` (Python) installed

## TypeScript example

```bash theme={null}
npm install x402-fetch viem
```

```typescript theme={null}
import { createWalletClient, http } from "viem";
import { privateKeyToAccount } from "viem/accounts";
import { base } from "viem/chains";
import { wrapFetchWithPayment } from "x402-fetch";

const account = privateKeyToAccount(process.env.PRIVATE_KEY as `0x${string}`);
const client = createWalletClient({ account, chain: base, transport: http() });

// Wrap fetch with x402 payment support
const fetchWithPayment = wrapFetchWithPayment(fetch, client);

// Make a paid call — no API key needed
const res = await fetchWithPayment(
  "https://data-tools.prd.arrays.org/api/v1/crypto/funding-rate?symbol=BTCUSDT"
);

console.log(await res.json());
```

That's it. The first call returns 402; `wrapFetchWithPayment` automatically signs, retries, and returns the data.

## Python example

```bash theme={null}
pip install x402-requests
```

```python theme={null}
import os
from x402_requests import X402Session
from eth_account import Account

account = Account.from_key(os.environ["PRIVATE_KEY"])
session = X402Session(account=account, chain="base")

res = session.get(
    "https://data-tools.prd.arrays.org/api/v1/crypto/funding-rate",
    params={"symbol": "BTCUSDT"},
)
print(res.json())
```

## Cost math

How much will it actually cost?

| Use case                         | Calls / month | Tier    | Cost         |
| -------------------------------- | ------------- | ------- | ------------ |
| Daily funding-rate snapshot      | 30            | \$0.008 | **\$0.24**   |
| Hourly funding-rate for 10 pairs | 7,200         | \$0.008 | **\$57.60**  |
| Crypto screener every 5 min      | 8,640         | \$0.03  | **\$259.20** |

<Tip>
  At sustained high volume, a [subscription plan](/pricing) usually becomes cheaper than per-call nanopayment. Mix both: subscription for steady workloads, Nanopayment for spikes.
</Tip>

## Troubleshooting

<AccordionGroup>
  <Accordion title="`Insufficient USDC balance`">
    Top up via Circle Gateway. The error response includes the exact amount needed.
  </Accordion>

  <Accordion title="`Unsupported chain`">
    Nanopayment supports 11 EVM chains. Check your wallet client is on Base, Ethereum, Arbitrum, Optimism, Polygon, or another supported chain.
  </Accordion>

  <Accordion title="`Signature invalid`">
    Make sure your wallet client uses the same account that holds the USDC. EIP-3009 requires the signer == token holder.
  </Accordion>
</AccordionGroup>