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Sample API Requests

If your app or platform processes stablecoin transactions, you’ll likely want a backend layer to help manage interactions with wallets and blockchain networks. Whether you’re sending payouts, confirming incoming payments, or logging transactions, these sample API patterns will give you a solid starting point. The examples below are written in JavaScript (Node.js/Express) but can be adapted to any stack. They assume you're using a provider like Infura, Alchemy, or a private RPC to connect to an EVM-compatible chain such as Ethereum, Polygon, or Arbitrum.

1. Check stablecoin balance (ERC-20)​

js
// GET /balance?address=0x123...&token=0xA0b8...
import Web3 from 'web3';
import erc20ABI from './erc20ABI.json'; // standard ERC-20 ABI

const web3 = new Web3(process.env.RPC_URL);

export async function getBalance(req, res) {
  const { address, token } = req.query;

  try {
    const contract = new web3.eth.Contract(erc20ABI, token);
    const rawBalance = await contract.methods.balanceOf(address).call();
    const balance = Number(rawBalance) / 10 ** 6; // For USDC: 6 decimals

    res.json({ address, token, balance });
  } catch (err) {
    res.status(500).json({ error: 'Could not fetch balance', details: err.message });
  }
}

2. Send a stablecoin transfer​

js
// POST /send
// body: { from, to, amount, token }

export async function sendStablecoin(req, res) {
  const { from, to, amount, token } = req.body;
  const contract = new web3.eth.Contract(erc20ABI, token);

  try {
    const amountRaw = web3.utils.toBN(amount * 10 ** 6); // USDC format
    const gas = await contract.methods.transfer(to, amountRaw).estimateGas({ from });

    const tx = await contract.methods
      .transfer(to, amountRaw)
      .send({ from, gas });

    res.json({ status: 'success', txHash: tx.transactionHash });
  } catch (err) {
    res.status(500).json({ error: 'Transfer failed', details: err.message });
  }
}

Note: This requires the private key to be loaded into a signer like Web3’s web3.eth.accounts.wallet, or handled through a secure service like Fireblocks or a custodian. Never expose private keys in plaintext.

3. Monitor for incoming payments​

To track incoming stablecoin transfers, you can use an event listener or webhook-style polling system.

js
const subscription = contract.events.Transfer({
  filter: { to: monitoredAddress },
}).on('data', (event) => {
  const { from, to, value } = event.returnValues;
  const amount = Number(value) / 10 ** 6;

  console.log(`Received ${amount} tokens from ${from}`);
});

For production systems, you can use services like:

  • Alchemy Notify for webhook alerts
  • The Graph to query blockchain events
  • Backend cron jobs that poll and log Transfer events at intervals

Suggested use cases​

  • Log wallet activity for user dashboards
  • Trigger actions after a payment is confirmed
  • Build internal tools to manage treasury or vendor payouts
  • Run batch payouts or scheduled transfers via API

Next steps​

  • Web3.js Send USDC – Direct example of frontend token transfers
  • Handling Business Funds – Organize wallet flows and team access
  • Stablecoin Accounting – How to log, track, and value on-chain payments