Making Your First x402 Payment

Step 1: Open Browser DevTools

Open your browser's Developer Tools to observe HTTP requests in real-time:

Chrome / Edge / Firefox:

• Press F12 or right-click → "Inspect"
• Click the Network tab
• Keep DevTools open

You'll see the HTTP 402 responses as they happen.

Step 2: Connect Your Wallet

With the starter kit running at http://localhost:3000:

1. Click "Connect Wallet"
2. Select Core Wallet
3. Ensure you're on Avalanche Fuji Testnet
4. Approve the connection
5. Your wallet address should display

Your wallet needs:

• Fuji USDC (payment token)

If missing, return here for faucet instructions.

Step 3: Request Protected Content

Click the "Pay $0.01" button on the Basic Tier card.

Observing HTTP 402

In DevTools Network tab, find the request to /api/basic:

• Status Code: 402 Payment Required
• Response Headers: Contains x-payment-request

The response body shows payment requirements:

{
    "x402Version": 1,
    "error": "X-PAYMENT header is required",
    "accepts": [
        {
            "scheme": "exact",
            "network": "eip155:43113",
            "maxAmountRequired": "10000",
            "resource": "http://localhost:3000/api/basic",
            "description": "",
            "mimeType": "application/json",
            "payTo": "0x41bB3178760536eAfE451aadF4eB5Ac76B9AfcF8",
            "maxTimeoutSeconds": 86400,
            "asset": "0x5425890298aed601595a70AB815c96711a31Bc65",
            "outputSchema": {
                "input": {
                    "type": "http",
                    "method": "GET",
                    "discoverable": true
                }
            },
            "extra": {
                "recipientAddress": "0x20E004611eb983B9De88dACc388Cb1461691d420",
                "facilitatorAddress": "0x41bB3178760536eAfE451aadF4eB5Ac76B9AfcF8",
                "name": "USD Coin",
                "version": "2",
                "primaryType": "TransferWithAuthorization"
            }
        }
    ]
}

Key Fields:

• maxAmountRequired: "10000" = $0.01 USDC (6 decimals)
• payTo: Merchant wallet receiving payment
• asset: USDC contract address on Fuji
• network: "avalanche-fuji"

This tells the client exactly what payment is required.

Step 4: Sign the Payment Authorization

Your wallet opens with a signature request. Click "Sign".

What You're Signing

You're signing an EIP-712 authorization (not sending a transaction). This authorizes the facilitator to move USDC from your wallet to the merchant using EIP-3009 (transferWithAuthorization).

The signature includes:

• From/To addresses
• Amount (0.01 USDC)
• USDC contract address
• Nonce (replay protection)
• Expiration timestamp
• Chain ID (43113)

Because the facilitator submits the transaction, users don't pay gas fees.

Step 5: Observe Payment Settlement

After signing, watch the payment flow:

Find the second request to /api/basic:

• Status Code: 200 OK (payment accepted)
• Request Headers: Contains X-PAYMENT with your signed authorization
• Response Headers: Contains X-PAYMENT-RESPONSE with the paid content

Step 6: Verify on Blockchain Explorer

Check the Transaction History on the Thirdweb dashboard to verify the on-chain settlement:

1. Open the Thirdweb Transaction History page
2. Find your recent transaction in the list
3. Click on the transaction hash to open the block explorer

You'll see the transaction showing 0.01 USDC transferred from your wallet to the merchant wallet.