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While USDC is commonly used with x402, the protocol supports any ERC-20 token. Configure your facilitator and middleware to accept multiple payment tokens.

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Prerequisites

  • Understanding of ERC-20 tokens
  • Basic knowledge of x402 protocol
  • A SKALE Chain endpoint
  • Node.js and npm installed

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Overview

x402 is token-agnostic and works with any ERC-20 compatible token. You can:
  1. Accept multiple payment tokens
  2. Allow users to choose their preferred token
  3. Configure different prices for different tokens
  4. Handle different token decimals

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Multiple Payment Options in Middleware

Configure your middleware to accept multiple tokens: 
import { createMiddleware } from "@faremeter/middleware/express";

const paywalled = await createMiddleware({
  facilitatorURL: "https://facilitator.dirtroad.dev",
  accepts: [
    [
      {
        scheme: "exact",
        network: "skale-base-sepolia",
        asset: "0x2e08028E3C4c2356572E096d8EF835cD5C6030bD",
        maxAmountRequired: "1.5",
        description: "SKALE USDC payment",
      },
      {
        scheme: "exact",
        network: "skale-base-sepolia",
        asset: "0x3ca0a49f511c2c89c4dcbbf1731120d8919050bf",
        maxAmountRequired: "1.5",
        description: "SKALE USDT payment",
      },
      {
        scheme: "exact",
        network: "skale-base-sepolia",
        asset: "0xf94056bd7f6965db3757e1b145f200b7346b4fc0",
        maxAmountRequired: "0.001",
        description: "SKALE WETH payment",
      },
    ],
  ],
});

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Facilitator Configuration

Configure your facilitator to handle multiple tokens: 
import { createFacilitator } from '@faremeter/facilitator';
import { createPaymentHandler } from '@faremeter/payment-evm';

const usdcHandler = createPaymentHandler({
  network: 'skale-base-sepolia',
  asset: '0x2e08028E3C4c2356572E096d8EF835cD5C6030bD',
  rpcUrl: 'YOUR_SKALE_RPC_URL',
});

const usdtHandler = createPaymentHandler({
  network: 'skale-base-sepolia',
  asset: '0x3ca0a49f511c2c89c4dcbbf1731120d8919050bf',
  rpcUrl: 'YOUR_SKALE_RPC_URL',
});

const facilitator = createFacilitator({
  network: 'skale-base-sepolia',
  paymentHandlers: [
    {
      scheme: 'exact',
      network: 'skale-base-sepolia',
      asset: '0x2e08028E3C4c2356572E096d8EF835cD5C6030bD',
      handler: usdcHandler,
    },
    {
      scheme: 'exact',
      network: 'skale-base-sepolia',
      asset: '0x3ca0a49f511c2c89c4dcbbf1731120d8919050bf',
      handler: usdtHandler,
    },
  ],
});

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Token Selection

Allow clients to choose their payment token: 
async function accessResource(url: string, preferredToken?: string) {
  const response = await fetch(url);
  
  if (response.status === 402) {
    const paymentInfo = await response.json();
    
    let selectedOption = paymentInfo.accepts[0];
    
    if (preferredToken) {
      const matchingOption = paymentInfo.accepts.find(
        (option) => option.asset?.toLowerCase() === preferredToken.toLowerCase()
      );
      if (matchingOption) {
        selectedOption = matchingOption;
      }
    }
    
    const payment = await x402Client.createPayment({
      ...selectedOption,
      resource: url,
    });
    
    await x402Client.settle(payment);
    
    const retryResponse = await fetch(url, {
      headers: {
        'X-PAYMENT': JSON.stringify(payment),
      },
    });
    
    return await retryResponse.json();
  }
  
  return await response.json();
}

​
Price Conversion

Handle different token prices: 
const tokenPrices = {
  '0x2e08028E3C4c2356572E096d8EF835cD5C6030bD': 1.0,  // USDC - Base price
  '0x3ca0a49f511c2c89c4dcbbf1731120d8919050bf': 1.0,  // USDT - Same as USDC
  '0xf94056bd7f6965db3757e1b145f200b7346b4fc0': 3000.0, // WETH - ETH price in USD
};

function calculateAmount(tokenAddress: string, usdAmount: number): string {
  const price = tokenPrices[tokenAddress.toLowerCase()];
  const tokenAmount = usdAmount / price;
  return tokenAmount.toFixed(6);
}

// Use in middleware accepts
const accepts = [
  {
    scheme: 'exact',
    network: 'skale-base-sepolia',
    asset: '0x2e08028E3C4c2356572E096d8EF835cD5C6030bD',
    maxAmountRequired: '1.5',
  },
  {
    scheme: 'exact',
    network: 'skale-base-sepolia',
    asset: '0xf94056bd7f6965db3757e1b145f200b7346b4fc0',
    maxAmountRequired: calculateAmount('0xf94056bd7f6965db3757e1b145f200b7346b4fc0', 1.5),
  },
];

​
Handling Different Decimals

const accepts = [
  {
    scheme: 'exact',
    network: 'skale-base-sepolia',
    asset: '0x2e08028E3C4c2356572E096d8EF835cD5C6030bD',
    maxAmountRequired: ethers.parseUnits('1.5', 6).toString(),
  },
  {
    scheme: 'exact',
    network: 'skale-base-sepolia',
    asset: '0xf94056bd7f6965db3757e1b145f200b7346b4fc0',
    maxAmountRequired: ethers.parseUnits('0.001', 18).toString(),
  },
];

​
Common Tokens on SKALE Base Sepolia

Popular tokens available on SKALE Base Sepolia:
  • USDC: 0x2e08028E3C4c2356572E096d8EF835cD5C6030bD - Stablecoin, 6 decimals
  • USDT: 0x3ca0a49f511c2c89c4dcbbf1731120d8919050bf - Stablecoin, 6 decimals
  • WBTC: 0x4512eacd4186b025186e1cf6cc0d89497c530e87 - Wrapped Bitcoin, 8 decimals
  • ETH (ERC-20): 0xD2Aaa00700000000000000000000000000000000 - Native ETH as ERC-20
  • WETH: 0xf94056bd7f6965db3757e1b145f200b7346b4fc0 - Wrapped ETH, 18 decimals
  • SKL: 0xaf2e0ff5b5f51553fdb34ce7f04a6c3201cee57b - SKALE Token, 18 decimals
  • AxiosUSD: 0x61a26022927096f444994dA1e53F0FD9487EAfcf - Test stablecoin

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Next Steps

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