Crossmint

This example demonstrates integration using Crossmint Smart Wallets with x402 v2. Perfect for applications needing smart wallet features and account abstraction.

Overview

Integrate Snack Money payments using Crossmint’s smart wallet infrastructure with x402 v2, using Crossmint’s API for signing operations.

Features

✅ Base network support
✅ Smart wallet infrastructure - Account abstraction
✅ API-based signing - Secure signature requests
✅ Developer-controlled signing - Full control
✅ x402 v2 integration - Latest protocol

Prerequisites

Node.js 18+
Crossmint account (Sign up)
Crossmint API key
Smart wallet with USDC balance on Base

Installation

npm install axios @x402/axios @x402/evm viem dotenv

Quick Start

1. Get Crossmint Credentials

Visit Crossmint Console
Create a project
Get your API key
Create a smart wallet

2. Set Up Environment

Create a .env file:

CROSSMINT_API_KEY=your_api_key
WALLET_LOCATOR=your_wallet_locator
SMART_WALLET_ADDRESS=your_smart_wallet_address
RECEIVER=your_x_username
AMOUNT=0.01

Important: The SMART_WALLET_ADDRESS should have USDC balance on Base network.

3. Implement Payment

Create base-send.ts:

import axios from "axios";
import { config } from "dotenv";
import { type Hex, type Address, type SignableMessage } from "viem";
import { toAccount } from "viem/accounts";
import { x402Client, wrapAxiosWithPayment, decodePaymentResponseHeader } from "@x402/axios";
import { registerExactEvmScheme } from "@x402/evm/exact/client";

config();

const crossmintApiKey = process.env.CROSSMINT_API_KEY as string;
const walletLocator = process.env.WALLET_LOCATOR as string;
const smartWalletAddress = process.env.SMART_WALLET_ADDRESS as string;
const receiver = process.env.RECEIVER as string;
const amount = parseFloat(process.env.AMOUNT || "0.01");

// Helper to request signatures from Crossmint API
async function requestCrossmintSignature(
  walletLocator: string,
  apiKey: string,
  signatureRequest: any
): Promise<Hex> {
  const createResponse = await axios.post(
    `https://www.crossmint.com/api/2022-06-09/wallets/${walletLocator}/signatures`,
    signatureRequest,
    {
      headers: {
        "X-API-KEY": apiKey,
        "Content-Type": "application/json"
      }
    }
  );

  const signatureId = createResponse.data.id;

  // Poll for signature
  let signature: string | null = null;
  let attempts = 0;
  const maxAttempts = 20;

  while (!signature && attempts < maxAttempts) {
    attempts++;
    const statusResponse = await axios.get(
      `https://www.crossmint.com/api/2022-06-09/wallets/${walletLocator}/signatures/${signatureId}`,
      { headers: { "X-API-KEY": apiKey } }
    );

    signature = statusResponse.data.outputSignature;
    if (signature) return signature as Hex;
    if (statusResponse.data.status === 'failed') {
      throw new Error(`Signature failed: ${JSON.stringify(statusResponse.data)}`);
    }
    await new Promise(resolve => setTimeout(resolve, 1000));
  }

  throw new Error(`Signature did not complete after ${maxAttempts} attempts`);
}

// Create a viem account that uses Crossmint's signature API
function createCrossmintAccount(
  address: Address,
  walletLocator: string,
  apiKey: string
) {
  const account = toAccount({
    address,
    async signMessage({ message }: { message: SignableMessage }): Promise<Hex> {
      const messageStr = typeof message === 'string' ? message : (message as any).raw || JSON.stringify(message);
      return requestCrossmintSignature(walletLocator, apiKey, {
        type: "evm-message",
        params: { message: messageStr, chain: "base" }
      });
    },
    signTransaction: async () => {
      throw new Error("Transaction signing not supported - use Crossmint transaction API");
    },
    signTypedData: async (typedData: any): Promise<Hex> => {
      return requestCrossmintSignature(walletLocator, apiKey, {
        type: "evm-typed-data",
        params: { typedData, chain: "base" }
      });
    }
  });

  return {
    ...account,
    sign: async ({ hash }: { hash: Hex }): Promise<Hex> => {
      return account.signMessage({ message: { raw: hash } as any });
    }
  } as any;
}

async function sendPayment() {
  console.log("🚀 Starting Snack Money payment with Crossmint Smart Wallet\n");
  console.log("ℹ️  Network: Base (EVM)\n");
  console.log(`✅ Smart Wallet Address: ${smartWalletAddress}`);
  console.log(`💡 Check balance: https://basescan.org/address/${smartWalletAddress}\n`);

  // Create Crossmint account
  const crossmintAccount = createCrossmintAccount(
    smartWalletAddress as Address,
    walletLocator,
    crossmintApiKey
  );

  // Create x402 client and register EVM scheme
  const client = new x402Client();
  registerExactEvmScheme(client, { signer: crossmintAccount });

  // Wrap axios with payment interceptor
  const api = wrapAxiosWithPayment(
    axios.create({ baseURL: "https://api.snack.money" }),
    client
  );

  console.log(`💸 Sending ${amount} USDC to @${receiver} on X via Base...\n`);

  try {
    const response = await api.post("/payments/x/pay", {
      amount,
      currency: "USDC",
      receiver,
      description: "Payment via Crossmint Smart Wallet (Base)"
    });

    console.log("✅ Payment successful!");
    console.log("\n📊 Response:", JSON.stringify(response.data, null, 2));

    const paymentResponseHeader = response.headers["payment-response"];
    if (paymentResponseHeader) {
      const paymentResponse = decodePaymentResponseHeader(paymentResponseHeader);
      console.log("\n🔐 Payment Response Details:", JSON.stringify(paymentResponse, null, 2));
    }

    if (response.data.data?.receipt) {
      console.log(`\n🧾 Receipt: ${response.data.data.receipt}`);
    }
  } catch (error: any) {
    console.error("❌ Payment failed:", error.response?.data || error.message);
    process.exit(1);
  }
}

sendPayment();

4. Run the Example

npm run base
# or
npx tsx base-send.ts

Expected Output

🚀 Starting Snack Money payment with Crossmint Smart Wallet

ℹ️  Network: Base (EVM)

✅ Smart Wallet Address: 0x...
💡 Check balance: https://basescan.org/address/0x...

🔐 Creating Crossmint account...

💸 Sending 0.01 USDC to @username on X via Base...

✅ Payment successful!

📊 Response: {
  "code": 200,
  "msg": "0.01 USDC sent successfully",
  "data": {
    "txn_id": "...",
    "amount": 0.01,
    "receipt": "https://snack.money/x/username?txn=..."
  }
}

How It Works

Create Crossmint Account: Build a viem-compatible account that uses Crossmint’s signature API
Register x402 EVM Scheme: Configure x402 client with the Crossmint signer
Wrap Axios: Add x402 payment interceptor
Send Payment: Make payment request
Auto Signatures: Crossmint API handles message and typed data signing
Success: Receive confirmation and receipt

Why Crossmint?

Benefits

Smart Wallets: Advanced wallet capabilities
Account Abstraction: Gasless transactions, batching
Viem Compatible: Standard interface
Developer Controlled: Full control over signing
Easy Integration: Simple SDK

Best For

Apps needing smart wallet features
Account abstraction requirements
Gasless transactions
Advanced wallet operations

Smart Wallet Features

Gasless Transactions

const wallet = await CrossmintSmartWallet.build({
  config: {
    chain: "base",
    apiKey: process.env.CROSSMINT_API_KEY!,
    gasless: true,  // Enable gasless transactions
  },
  signer: {
    type: "DEVELOPER_CONTROLLED",
    secret: process.env.CROSSMINT_SIGNER_SECRET!,
  },
});

Transaction Batching

// Batch multiple operations
await wallet.sendBatchTransaction([
  { to: address1, data: "0x..." },
  { to: address2, data: "0x..." },
]);

Supported Platforms

// X (Twitter)
await api.post("/payments/x/pay", {
  amount: 0.01,
  receiver: "username",
  currency: "USDC"
});

// Farcaster
await api.post("/payments/farcaster/pay", {
  amount: 0.5,
  receiver: "username",
  currency: "USDC"
});

// GitHub
await api.post("/payments/github/pay", {
  amount: 1.0,
  receiver: "username",
  currency: "USDC"
});

Error Handling

try {
  const response = await api.post("/payments/x/pay", {
    amount: 0.01,
    currency: "USDC",
    receiver: "username"
  });
  console.log("Success:", response.data);
} catch (error) {
  console.error("Payment failed:", error);

  // Handle Crossmint-specific errors
  if (error.message.includes("insufficient funds")) {
    console.error("Smart wallet needs more USDC");
  }
}

Wallet Management

Check Balance

const balance = await wallet.getBalance();
console.log("Wallet balance:", balance);

Get Wallet Info

console.log("Address:", wallet.address);
console.log("Chain:", wallet.chain);

Full Example Repository

View on GitHub → Includes:

Complete implementation
Smart wallet setup
Configuration guide
Detailed README

Next Steps

Try axios - Simplest integration
Crossmint Docs - Learn more
API Reference - Complete API docs

Dependencies

{
  "dependencies": {
    "axios": "^1.7.9",
    "@x402/axios": "^2.0.0",
    "@x402/evm": "^2.0.0",
    "viem": "^2.39.3",
    "dotenv": "^16.4.7"
  },
  "devDependencies": {
    "@types/node": "^22.0.0",
    "typescript": "^5.9.0"
  }
}

Introduction

CLI

SDK Examples

Overview

Features

Prerequisites

Installation

Quick Start

1. Get Crossmint Credentials

2. Set Up Environment

3. Implement Payment

4. Run the Example

Expected Output

How It Works

Why Crossmint?

Benefits

Best For

Smart Wallet Features

Gasless Transactions

Transaction Batching

Supported Platforms

Error Handling

Wallet Management

Check Balance

Get Wallet Info

Full Example Repository

Next Steps

Dependencies

Learn More

​Overview

​Features

​Prerequisites

​Installation

​Quick Start

​1. Get Crossmint Credentials

​2. Set Up Environment

​3. Implement Payment

​4. Run the Example

​Expected Output

​How It Works

​Why Crossmint?

​Benefits

​Best For

​Smart Wallet Features

​Gasless Transactions

​Transaction Batching

​Supported Platforms

​Error Handling

​Wallet Management

​Check Balance

​Get Wallet Info

​Full Example Repository

​Next Steps

​Dependencies

​Learn More

Overview

Features

Prerequisites

Installation

Quick Start

1. Get Crossmint Credentials

2. Set Up Environment

3. Implement Payment

4. Run the Example

Expected Output

How It Works

Why Crossmint?

Benefits

Best For

Smart Wallet Features

Gasless Transactions

Transaction Batching

Supported Platforms

Error Handling

Wallet Management

Check Balance

Get Wallet Info

Full Example Repository

Next Steps

Dependencies

Learn More