How to setup the first account in a private network?

Question

Hi have setup a private network. Now how do I create the first account so I can start using the network? I have tried the following:

const Stellar = require('stellar-sdk')

const NETWORK_PASSPHRASE = "TEST Stellar Network ; June 2020";
var server = new Stellar.Server('http://localhost:8000', {allowHttp: true});

let sourceKeys = Stellar.Keypair.master(NETWORK_PASSPHRASE);
console.log("sourceKeys Public key : ", sourceKeys.publicKey());
console.log("sourceKeys Secret : ", sourceKeys.secret());

try{
    const pk = "GAABRIRAI3QHVSGAPWNFMOMWEMG7ATCQGRO2B4F72WYKVR46JYEWSOLF"
    let sourceKeys = Stellar.Keypair.master(NETWORK_PASSPHRASE);

    server.loadAccount(sourceKeys.publicKey())
        .then(function(sourceAccount) {
            let txn = new Stellar.TransactionBuilder(sourceAccount, opts={fee: 1, networkPassphrase: NETWORK_PASSPHRASE})
                .addOperation(
                    Stellar.Operation.createAccount({
                        destination: pk,
                        startingBalance: "100"}))
                .addMemo(Stellar.Memo.text('Test Transaction'))
                .setTimeout(5)
                .build();
            txn.sign(sourceKeys);
            return server.submitTransaction(txn);
        })
        .then(function(result) {
            console.log(JSON.stringify(result))
        })
        .catch(function(error) {
            console.error('Something went wrong!', error);
        });

}catch(err){
    console.error("ERROR :", error)
}

but I keep getting the following error:

Error: Request failed with status code 400
    at createError (C:\dev\stellar\stellar-wallet\node_modules\axios\lib\core\createError.js:16:15)
    at settle (C:\dev\stellar\stellar-wallet\node_modules\axios\lib\core\settle.js:17:12)
    at IncomingMessage.handleStreamEnd (C:\dev\stellar\stellar-wallet\node_modules\axios\lib\adapters\http.js:236:11)
    at IncomingMessage.emit (events.js:203:15)
    at endReadableNT (_stream_readable.js:1145:12)
    at process._tickCallback (internal/process/next_tick.js:63:19)

UPDATE 1

I have tried to use GO client and it is posting the transaction (I can see the transaction on horizon) but it is returning an error:

strconv.ParseInt: parsing "": invalid syntax

I personally think that there is a bug on the GO client library for horizon, since for some reason it is failing to parse the field "fee_charged".

Any help would be appreciated