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The Problem

Every crypto payment integration follows the same painful pattern:

Read blockchain docs for each chain
Implement RPC calls
Handle WebSocket reconnections
Parse transaction data
Calculate correct decimals (looking at you, BSC USDT with 18 decimals while everyone else uses 6)
Build block explorer URLs
Write confirmation logic

And that's just one chain. What about the other 8 your client wants?

The Solution: payx3

const { watchAll } = require("payx3");

await watchAll({
  btcAddress: "bc1qar0srrr7xfkvy5l643lydnw9re59gtzzwf5mdq",
  evmAddress: "0xb2C65C9C98C2216099A37AF7FE12A93b8A37AFBd",
  solAddress: "CbWki5xkrnde7TYj11jDWNEJ3h7bRTmk5Q22uANNfEt",
  infuraKey: "YOUR_KEY",

  onPayment: (payment) => {
    console.log(`${payment.amount} ${payment.symbol} received on ${payment.chain}`);
    // Fires for EVERYTHING: BTC, ETH, BNB, SOL, USDT, USDC...
  },
});

One call. All chains. All tokens. Real-time.

What You Get

🔑 Wallet Generation

Generate a BIP-39 mnemonic and derive addresses for all supported chains simultaneously:

const { generateMnemonic, deriveAll } = require("payx3");

const mnemonic = generateMnemonic(128);  // 12 words
const wallet = await deriveAll(mnemonic);

console.log(wallet.bitcoin[2].address);  // bc1... Native SegWit
console.log(wallet.evm.address);         // 0x... For ETH, BNB, MATIC, AVAX, ARB, OP
console.log(wallet.solana.address);      // Solana address

👁️ Real-time Payment Watching

Chain	Native Token	Supported Tokens
Bitcoin	BTC	—
Ethereum	ETH	USDT, USDC, DAI, WBTC, WETH, LINK, UNI, AAVE, SHIB
BNB Chain	BNB	USDT, USDC, DAI, LINK
Polygon	MATIC	USDT, USDC, DAI, WBTC, WETH, LINK, UNI, AAVE
Avalanche	AVAX	USDT, USDC, DAI, WBTC, WETH, LINK, AAVE
Arbitrum	ETH	USDT, USDC, DAI, WBTC, WETH, LINK, UNI
Optimism	ETH	USDT, USDC, DAI, WBTC, WETH, LINK
Solana	SOL	Any SPL token

🎯 Watch Any Custom ERC-20

const { watchToken } = require("payx3");

watchToken({
  address: "0x...",
  infuraKey: "YOUR_KEY",
  chain: "ETH",
  contractAddress: "0x6982508145454Ce325dDbE47a25d4ec3d2311933",  // PEPE
  decimals: 18,
  symbol: "PEPE",
  name: "Pepe",
  onPayment: (p) => console.log(`${p.amount} PEPE received!`),
});

Payment Object

Every callback receives a consistent object regardless of chain:

{
  chain: "Ethereum",
  chainSymbol: "ETH",
  symbol: "USDT",
  name: "Tether USD",
  amount: "100.50",
  txHash: "0xa1b2c3...",
  status: "unconfirmed",      // or "confirmed"
  explorerUrl: "https://etherscan.io/tx/0xa1b2c3...",
  contract: "0xdAC17F...",    // null for native coins
  timestamp: 1715000000000,
  blockNumber: 19500000        // onConfirmed only
}

CLI Tool

No code? No problem. Install globally:

npm install -g payx3

Generate a wallet:

payx3 generate

Watch for payments using config.json:

{
  "infuraKey": "YOUR_INFURA_KEY",
  "addresses": {
    "BTC": "bc1q...",
    "EVM": "0x...",
    "SOL": "CbWk..."
  }
}

payx3 watch

Or watch specific addresses inline:

payx3 watch --btc bc1q... --evm 0x... --sol CbWk... --key YOUR_INFURA_KEY

REST API Server

Run as a full API server:

node examples/server.js
# Server running on http://localhost:3000

Endpoints

Method	Endpoint	Description
`POST`	`/wallet/create`	Generate wallet + addresses
`POST`	`/watch/btc`	Watch BTC address
`POST`	`/watch/eth`	Watch ETH
`POST`	`/watch/bnb`	Watch BNB
`POST`	`/watch/polygon`	Watch MATIC
`POST`	`/watch/avalanche`	Watch AVAX
`POST`	`/watch/arbitrum`	Watch ETH on Arbitrum
`POST`	`/watch/optimism`	Watch ETH on Optimism
`POST`	`/watch/sol`	Watch SOL + SPL tokens
`POST`	`/watch/usdt`	Watch USDT (any chain)
`POST`	`/watch/usdc`	Watch USDC (any chain)
`POST`	`/watch/token`	Watch any ERC-20
`POST`	`/watch/all`	Watch everything at once
`GET`	`/payments`	List all received payments
`DELETE`	`/watch/:id`	Stop a watcher

Real-World Examples

E-commerce Checkout

const { generateMnemonic, deriveAll, watchAll } = require("payx3");

async function createPaymentSession(orderId, amountUSD) {
  // Generate a fresh wallet for this order
  const mnemonic = generateMnemonic(128);
  const wallet = await deriveAll(mnemonic);

  // Store mnemonic temporarily (in DB with orderId)
  await db.saveOrderWallet(orderId, mnemonic);

  // Start watching
  watchAll({
    btcAddress: wallet.bitcoin[2].address,
    evmAddress: wallet.evm.address,
    solAddress: wallet.solana.address,
    infuraKey: process.env.INFURA_KEY,

    onPayment: async (payment) => {
      // Mark order as paid
      await db.updateOrderStatus(orderId, "paid", payment);

      // Send confirmation email
      await email.send(orderEmail, `Payment received: ${payment.amount} ${payment.symbol}`);

      // Trigger fulfillment webhook
      await axios.post(fulfillmentUrl, { orderId, payment });
    },
  });

  return {
    addresses: {
      BTC: wallet.bitcoin[2].address,
      EVM: wallet.evm.address,
      SOL: wallet.solana.address,
    },
  };
}

Subscription Payments

const { watchUSDC } = require("payx3");

// Watch for $50 USDC monthly subscription payments
watchUSDC({
  address: companyWallet,
  infuraKey: process.env.INFURA_KEY,
  chain: "ETH",

  onPayment: async (payment) => {
    if (parseFloat(payment.amount) >= 50) {
      // Find user by transaction sender
      const user = await db.findUserByAddress(payment.from);
      if (user) {
        // Extend subscription by 30 days
        await db.extendSubscription(user.id, 30);

        // Send receipt
        await email.send(user.email, `Subscription renewed — ${payment.amount} USDC`);
      }
    }
  },
});

Why payx3?

✅ No Private Keys Needed

You never share private keys. The library only reads blockchain data. Your funds stay where they belong.

✅ Automatic Decimal Handling

USDT has 6 decimals on Ethereum but 18 on BNB Chain. payx3 handles this automatically. You always get human-readable amounts.

✅ Built-in Reconnection

WebSockets disconnect? payx3 reconnects automatically. Your payment detection never stops.

✅ 0→1 in 5 Minutes

From npm install to watching payments on 8 chains. No blockchain experience required.

Installation

npm install payx3

Get a free Infura key: https://app.infura.io/register

GitHub & Documentation

github.com/susheelhbti/payx3

Full API documentation
Examples for every chain and token
REST API server example
MIT license — free for commercial use

Support the Project

If payx3 saves you development time, consider:

⭐ Starring the repo on GitHub

🐛 Reporting issues you find

🔧 Submitting PRs for new chains or tokens

💬 Sharing with other developers

About the Author

I'm Susheel, a blockchain developer available for freelance and full-time work.

Need a custom integration? Multi-chain payment system? Web3 infrastructure?

📧 [email protected]

payx3: Multi-Chain Crypto Payment SDK You've Been Waiting For