Baby's First x402 Payment with Base

You've heard about x402. Agents paying for APIs with crypto. Sounds cool, but you've never actually done it. This guide walks you through your first payment — from zero to "holy shit, it worked" in about 10 minutes.

We'll use AgentUtil as our test API and Base as our network. By the end, you'll have made a real x402 payment and gotten real data back.

What You'll Need

• A computer with Node.js installed
• $5 worth of USDC (or less — we're making penny payments)
• 10 minutes

That's it. No accounts to create, no API keys to manage.

Step 1: Get a Wallet

You need a wallet that can hold USDC on Base. The easiest option is Coinbase Wallet.

Option A: Coinbase Wallet (Mobile)

1. Download Coinbase Wallet app (not the main Coinbase app)
2. Create a new wallet
3. Write down your recovery phrase somewhere safe
4. Switch to Base network in settings

Option B: MetaMask (Browser)

1. Install MetaMask browser extension
2. Create a new wallet
3. Add Base network:
   • Network Name: Base
   • RPC URL: https://mainnet.base.org
   • Chain ID: 8453
   • Currency: ETH
   • Explorer: https://basescan.org

Step 2: Get USDC on Base

You need USDC (a stablecoin worth $1) on the Base network.

From Coinbase

If you have a Coinbase account:

1. Buy USDC on Coinbase
2. Go to Send
3. Enter your wallet address
4. Important: Select "Base" as the network
5. Send $5-10 worth

Should arrive in a few seconds.

From Another Exchange

Most exchanges now support Base withdrawals. Look for "Base" or "Base Mainnet" when withdrawing USDC.

Bridge from Ethereum

If you have USDC on Ethereum mainnet:

1. Go to bridge.base.org
2. Connect your wallet
3. Select USDC and the amount
4. Bridge to Base

Takes a few minutes and costs some ETH gas.

Step 3: Install the x402 Client

Open your terminal:

npm install -g @x402/client

This gives you a command-line tool for making x402 payments.

Step 4: Connect Your Wallet

The x402 client needs access to your wallet to sign payments.

Export Your Private Key

Warning: Your private key controls your money. Never share it. Never paste it in a website. Only use it in tools you trust.

In MetaMask:

1. Click the three dots on your account
2. Account details → Export private key
3. Enter your password
4. Copy the key

Set it as an environment variable:

export X402_PRIVATE_KEY="your-private-key-here"

Or create a .env file:

echo "X402_PRIVATE_KEY=your-private-key-here" > ~/.x402env

Step 5: Make Your First Payment

Let's verify an email address. This costs $0.01.

x402 pay https://api.agentutil.dev/v1/tools/email.verify/tasks \
  --body '{"email": "test@gmail.com"}'

What happens:

1. Client sends POST request
2. Server returns 402 with payment details
3. Client signs USDC transfer
4. Client retries with payment proof
5. Server validates and returns result

You should see:

{
  "task_id": "task_abc123",
  "status": "pending",
  "poll_url": "/v1/tasks/task_abc123"
}

Then poll for the result:

curl https://api.agentutil.dev/v1/tasks/task_abc123

{
  "status": "complete",
  "result": {
    "email": "test@gmail.com",
    "deliverable": true,
    "is_free_email": true,
    "is_disposable": false,
    "quality_score": 0.95
  }
}

Congrats! You just made an x402 payment. Check your wallet — you're $0.01 lighter.

Step 6: Try More APIs

Now that you're set up, try some other tools:

DNS Lookup ($0.002)

x402 pay https://api.agentutil.dev/v1/tools/dns.lookup/tasks \
  --body '{"domain": "google.com"}'

IP Geolocation ($0.005)

x402 pay https://api.agentutil.dev/v1/tools/ip.geolocate/tasks \
  --body '{"ip": "8.8.8.8"}'

Geocoding ($0.005)

x402 pay https://api.agentutil.dev/v1/tools/geo.locate/tasks \
  --body '{"address": "Empire State Building, NYC"}'

Each one: request → 402 → pay → result. Same pattern every time.

What Just Happened?

Let's break down the magic:

The 402 Response

When you first hit the API, it returns:

HTTP/1.1 402 Payment Required
X-Payment: eyJhbW91bnQiOiIwLjAxIiwiY3VycmVuY3kiOiJVU0RDIi4uLn0=
X-Payment-Network: base
X-Payment-Address: 0x124CA4b34041D33914f94Cb5Fbaa5e4075EB08D7

The X-Payment header contains encoded payment details: how much, where to send it, and a nonce to prevent replay attacks.

The Payment

Your client decoded those details and signed a USDC transfer:

• From: Your wallet
• To: AgentUtil's wallet
• Amount: $0.01 USDC
• Network: Base

The signature proves you authorized the payment. The client sent this signature back with the retry request.

The Settlement

AgentUtil's server verified your signature and trusted that the payment would settle. A "facilitator" (usually Coinbase) handles the actual onchain transfer in the background.

You didn't have to wait for blockchain confirmation. The cryptographic signature was proof enough.

Check Your Payment History

See what you've spent:

x402 history

Or check the Base block explorer directly. Go to basescan.org, paste your wallet address, and look at the USDC transfers.

Every payment is onchain and auditable.

Troubleshooting

"Insufficient balance"

You need USDC on Base, not ETH, not USDC on Ethereum, not anything else. Check:

1. You're on Base network (chain ID 8453)
2. You have USDC (not USD, not USDbC)
3. Balance is enough for the payment + a tiny bit extra

"Invalid signature"

Usually means:

• Wrong private key
• Wrong network configured
• Payment expired (they're valid for ~5 minutes)

Try again — payments have short expiry windows.

"Network error"

The API or facilitator might be temporarily down. Wait a minute and retry.

Payment went through but no data

The API returned a task_id. You need to poll for the result:

curl https://api.agentutil.dev/v1/tasks/YOUR_TASK_ID

What's Next?

Give Your AI Agent a Wallet

The real power of x402 is autonomous payments. Your AI agent can have its own wallet and pay for APIs without human intervention.

See: Setting Up an x402 Wallet for Your AI Agent

Build Your Own x402 API

Want to accept x402 payments? It's easier than you think.

See: How to Test x402 APIs

Understand the Protocol

Dive deeper into how x402 works under the hood.

See: How x402 Works

Quick Reference

Base URL: https://api.agentutil.dev

---

You did it. Your first x402 payment. No account, no API key, no invoice — just crypto and an API call. Welcome to the future of machine-to-machine payments.

Questions? Email silas@agentutil.dev