在得到以下错误所有的时间：
资金不足。您尝试发送交易的帐户没有足够的资金。需要2500000000000000并获得：0.
我从我的txData中注解掉了gacPrice，如下所示：

const txData = {
        nonce: web3.utils.toHex(txCount),
        gasLimit: web3.utils.toHex(40000),
        //gasPrice: web3.utils.toHex(10e9),
        to: addressTo,
        from: addressFrom,
        data: functionAbi
}

现在我得到了一个tx hash的结果，但是这个tx hash不能通过etherscan或任何其他blockexplorer定位。我还能做什么来成功地在Kovan上执行交易？这是我的智能合约：

pragma solidity ^0.4.24;

contract Test2 {
    address public bank;

    struct Box {
        uint size;
    }
    Box public box;

    constructor() public {
        box.size = 3;
        bank = 0xa2079636...;
    }

    function changeBox(uint _change) public {
        box.size = _change;
    }

    function getBox() public returns (uint) {
        return box.size;
    }  
}

下面是我如何通过web3.js执行它（完整代码）：

const Web3 = require('web3')
const Tx = require('ethereumjs-tx')

const web3 = new Web3(new Web3.providers.HttpProvider('https://kovan.infura.io/apikey'))
const addressFrom = '0x002D18...'
const privKey = '240462...'
const addressTo = '0x36075430619b21Fff798454e2D5C81E9C18DEe81'

var contractABI = new web3.eth.Contract(
    [...abi...], addressTo);

const contractFunction = contractABI.methods.changeBox(5);
const functionAbi = contractFunction.encodeABI();

function sendSigned(txData, callback) {
    //const privateKey = new Buffer(config.privKey, 'hex')
    const privateKey = Buffer.from(privKey, 'hex');
    const transaction = new Tx(txData)
    transaction.sign(privateKey)
    const serializedTx = transaction.serialize().toString('hex')
    web3.eth.sendSignedTransaction('0x' + serializedTx, callback)
}

web3.eth.getTransactionCount(addressFrom).then(txCount => {
    // construct the transaction data
    const txData = {
        nonce: web3.utils.toHex(txCount),
        gasLimit: web3.utils.toHex(40000),
        //gasPrice: web3.utils.toHex(10e9), // 10 Gwei
        to: addressTo,
        from: addressFrom,
        data: functionAbi
        //value: web3.utils.toHex(web3.utils.toWei(123, 'wei'))
  }

    sendSigned(txData, function(err, result) {
        if (err) return console.log('error', err)
        console.log('sent', result)
    })

})