Why txHash in sendSignedTransaction giving Undefined value on sending on rinkeby testnet

Question

let Tx= require('ethereumjs-tx').Transaction;
const Web3= require('web3');
const url='https://rinkeby.infura.io/v3/d4dbc79ea192404fb42689cc55ce2fc0';
const web3 =new Web3(url);

const account1= '0x0B872d2A7F3Ca3bD24Ab1A9fe8FBC8059Ec32b5F';
const account2='0x20107D4a4e8BB5D50800288029ad58cE929D2c56';

//web3.eth.getBalance(account1,(err,bal)=>{ console.log(web3.utils.fromWei(bal,"ether"))});

//web3.eth.getBalance(account2,(err,bal)=>{ console.log(web3.utils.fromWei(bal,"ether"))});

const privatekey1 = new Buffer('A337E5C704CF4187C0CECF4A6E38AD42182B4D038EB8615E239216C5164FEB40','hex');
//const privatekey2 = Buffer.from(process.env.PRIVATE_KEY_2,'hex');

web3.eth.getTransactionCount(account1,async (err,txCount)=>{

//console.log(txCount);

//Build the transaction

const txObject ={
    nonce:web3.utils.toHex(txCount+1),
    to:account2,
    value:web3.utils.toHex(web3.utils.toWei('1',"ether")),
    gasLimit:web3.utils.toHex(210000),
    gasPrice:web3.utils.toHex(web3.utils.toWei('10',"gwei"))
}

//console.log(txObject);

//sign the transaction
const tx = new Tx(txObject);
tx.sign(privatekey1);

const serializeTransaction = tx.serialize();
const raw= '0x'+ serializeTransaction.toString('hex');

web3.eth.sendSignedTransaction(raw,(err,txHash)=>{
  console.log(txHash);
})

Answer 1

You just need to specify you are in the testnet

const tx = new Tx(txObject, {chain: 'rinkeby'});

Answer 2

You may need to specific the value for from of the tnx also as below

const txObject ={
    from: account1,
    nonce: web3.utils.toHex(txCount+1),
    to: account2,
    value: web3.utils.toHex(web3.utils.toWei('1',"ether")),
    gasLimit: web3.utils.toHex(21000),
    gasPrice: web3.utils.toHex(web3.utils.toWei('10',"gwei"))
}

And make sure that the prikey used to sign the tnx is belong to account1. It'd better to use ethereumjs-util to get address from privatekey as below

const util = require('ethereumjs-util'); 
const fromAddress = '0x' + util.privateToAddress(privkey).toString('hex');

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By the way, we only need 21000 for sending tnx, not so much like 210000