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susheel kumar
susheel kumar

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

#blockchain #javascript #showdev #web3

The Problem

Every crypto payment integration follows the same painful pattern:

  1. Read blockchain docs for each chain
  2. Implement RPC calls
  3. Handle WebSocket reconnections
  4. Parse transaction data
  5. Calculate correct decimals (looking at you, BSC USDT with 18 decimals while everyone else uses 6)
  6. Build block explorer URLs
  7. 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...
  },
});
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One call. All chains. All tokens. Real-time.

What You Get

πŸ”‘ 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
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πŸ‘οΈ Real-time Payment Watching

Chain Native Token Supported Tokens
Bitcoin BTC β€”
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!`),
});
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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
}
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CLI Tool

No code? No problem. Install globally:

npm install -g payx3
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Generate a wallet:

payx3 generate
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Watch for payments using config.json:

{
  "infuraKey": "YOUR_INFURA_KEY",
  "addresses": {
    "BTC": "bc1q...",
    "EVM": "0x...",
    "SOL": "CbWk..."
  }
}
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payx3 watch
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Or watch specific addresses inline:

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

Run as a full API server:

node examples/server.js
# Server running on http://localhost:3000
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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,
    },
  };
}
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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 β€” ${payment.amount} USDC`);
      }
    }
  },
});
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Why payx3?

βœ… No Private Keys Needed

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

βœ… Automatic Decimal Handling

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

βœ… Built-in Reconnection

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

βœ… 0β†’1 in 5 Minutes

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

Installation 

npm install payx3
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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 β€” free for commercial use

Support the Project

If payx3 saves you development time, consider:

⭐ Starring the repo on GitHub

πŸ› Reporting issues you find

πŸ”§ Submitting PRs for new chains or tokens

πŸ’¬ 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?

πŸ“§ susheelhbti@gmail.com

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