b402-sdk

Accept crypto payments on Binance Smart Chain with zero gas fees for users.

Installation

npm install b402-sdk ethers@6

Quick Start

import { B402 } from 'b402-sdk';
import { Wallet } from 'ethers';

// User's wallet
const wallet = new Wallet(process.env.PRIVATE_KEY!);

// Create B402 client
const b402 = new B402('mainnet');

// Send payment (user pays ZERO gas!)
const result = await b402.pay(wallet, {
  amount: '0.01',        // Amount in human-readable format
  token: 'USD1',         // USD1, USDT, or USDC
  recipient: '0x...'     // Seller's wallet address
});

if (result.success) {
  console.log('Payment sent!', result.txHash);
  // View on BSCScan: https://bscscan.com/tx/${result.txHash}
}

How It Works

1. User signs payment authorization with MetaMask (EIP-712) - FREE
2. B402 facilitator validates signature
3. Facilitator submits transaction on-chain and pays gas (~$0.003)
4. Payment settles in <3 seconds

User pays ZERO gas fees.

Supported Tokens

Mainnet (BSC)

• USD1 - World Liberty Financial stablecoin
• USDT - Tether USD
• USDC - USD Coin

Testnet (BSC Testnet)

• USDT - Testnet USDT

Before First Payment

Users need to approve the B402 relayer contract once:

import { Contract } from 'ethers';

const usd1 = new Contract(
  '0x8d0d000ee44948fc98c9b98a4fa4921476f08b0d',  // USD1 on BSC
  ['function approve(address spender, uint256 amount)'],
  wallet
);

await usd1.approve(
  '0xE1C2830d5DDd6B49E9c46EbE03a98Cb44CD8eA5a',  // B402 Relayer
  '115792089237316195423570985008687907853269984665640564039457584007913129639935'  // Max approval
);

After this one-time approval, all future payments are instant and gasless!

API Reference

new B402(network?, facilitatorUrl?)

Create B402 client.

• network: 'mainnet' or 'testnet' (default: 'mainnet')
• facilitatorUrl: Custom facilitator URL (optional)

b402.pay(wallet, options)

Send payment.

Parameters:

• wallet: ethers.js Wallet object
• options.amount: Amount as string (e.g., '0.01')
• options.token: 'USD1' | 'USDT' | 'USDC'
• options.recipient: Seller's wallet address
• options.timeoutSeconds: Payment validity period (default: 3600)

Returns:

{
  success: boolean;
  txHash?: string;
  error?: string;
  payer: string;
  recipient: string;
  amount: string;
  token: string;
}

Example: Complete Payment Flow

import { B402 } from 'b402-sdk';
import { Wallet, Contract, JsonRpcProvider } from 'ethers';

async function sendPayment() {
  // Setup
  const provider = new JsonRpcProvider('https://bsc-dataseed1.binance.org');
  const wallet = new Wallet(process.env.PRIVATE_KEY!, provider);
  
  // Check USD1 balance
  const usd1 = new Contract(
    '0x8d0d000ee44948fc98c9b98a4fa4921476f08b0d',
    ['function balanceOf(address) view returns (uint256)',
     'function allowance(address,address) view returns (uint256)',
     'function approve(address,uint256) returns (bool)'],
    wallet
  );
  
  const balance = await usd1.balanceOf(wallet.address);
  console.log('Balance:', balance.toString());
  
  // Check/approve relayer
  const allowance = await usd1.allowance(
    wallet.address,
    '0xE1C2830d5DDd6B49E9c46EbE03a98Cb44CD8eA5a'
  );
  
  if (allowance === 0n) {
    console.log('Approving relayer...');
    const tx = await usd1.approve(
      '0xE1C2830d5DDd6B49E9c46EbE03a98Cb44CD8eA5a',
      '115792089237316195423570985008687907853269984665640564039457584007913129639935'
    );
    await tx.wait();
    console.log('Approved!');
  }
  
  // Send payment
  const b402 = new B402('mainnet');
  const result = await b402.pay(wallet, {
    amount: '0.01',
    token: 'USD1',
    recipient: '0x96625c0e209b4e0d4741d8a3ffb6b91c0da6fa5f'
  });
  
  if (result.success) {
    console.log('Payment successful!');
    console.log('TX:', result.txHash);
    console.log('View on BSCScan: https://bscscan.com/tx/' + result.txHash);
  } else {
    console.error('Payment failed:', result.error);
  }
}

sendPayment();

Live Example

Check out this real transaction on BSC mainnet: https://bscscan.com/tx/0x665845a92fd09e4673dac65ae23725cd58d2350d0347d2fca921bbe4a96eab30

• User paid: $0.00 gas
• Facilitator paid: $0.003 gas
• Payment: 0.01 USD1 transferred instantly

Security

• EIP-712 signatures - Industry standard (Uniswap, OpenSea)
• Nonce system - Prevents replay attacks
• Time-bounded - Authorizations expire
• On-chain verification - Contract verifies signatures before transfer

Network Details

Mainnet

• Chain ID: 56
• RPC: https://bsc-dataseed1.binance.org
• B402 Relayer: 0xE1C2830d5DDd6B49E9c46EbE03a98Cb44CD8eA5a
• USD1: 0x8d0d000ee44948fc98c9b98a4fa4921476f08b0d
• USDT: 0x55d398326f99059fF775485246999027B3197955
• USDC: 0x8AC76a51cc950d9822D68b83fE1Ad97B32Cd580d

Testnet

• Chain ID: 97
• RPC: https://data-seed-prebsc-1-s1.binance.org:8545
• B402 Relayer: 0x62150F2c3A29fDA8bCf22c0F22Eb17270FCBb78A
• USDT: 0x337610d27c682E347C9cD60BD4b3b107C9d34dDd

License

MIT

Links

• Homepage: https://b402.ai
• GitHub: https://github.com/vistara-labs/b402-protocol
• NPM: https://npmjs.com/package/b402-sdk