Error: nonce has already been used (error={"code":-32000,"message":"nonce too low"})

// Get the correct nonce before sending
const nonce = await provider.getTransactionCount(wallet.address, 'pending');
const tx = await wallet.sendTransaction({ ...txData, nonce });

Error: insufficient funds for intrinsic transaction cost

const balance = await provider.getBalance(wallet.address);
const gasEstimate = await provider.estimateGas(txData);
const feeData = await provider.getFeeData();
const totalCost = gasEstimate * feeData.gasPrice! + txData.value;
if (balance < totalCost) {
  console.error(`Need ${ethers.formatEther(totalCost)} ETH, have ${ethers.formatEther(balance)}`);
}

Error: execution reverted (reason="ERC20: transfer amount exceeds balance")

try {
  const gas = await contract.transfer.estimateGas(to, amount);
} catch (err) {
  console.error('Revert reason:', err.reason);
  // Check: sufficient token balance, approvals, contract state
}

Error: 429 Too Many Requests

async function retryRpc<T>(fn: () => Promise<T>, retries = 3): Promise<T> {
  for (let i = 0; i < retries; i++) {
    try { return await fn(); }
    catch (err: any) {
      if (err.code === 'SERVER_ERROR' && i < retries - 1) {
        await new Promise(r => setTimeout(r, 1000 * Math.pow(2, i)));
        continue;
      }
      throw err;
    }
  }
  throw new Error('Max retries');
}

Error: Method not found — qn_getTokenMetadataByContractAddress

Error: WebSocket connection closed unexpectedly

const wsProvider = new ethers.WebSocketProvider(process.env.QUICKNODE_WSS);
wsProvider.websocket.on('close', () => {
  console.log('WebSocket closed, reconnecting...');
  // Reconnect logic
});