JSON request error "invalid username"

app.js

const encode = encodeURIComponent
const url = "https://www.f-list.net/json/getApiTicket.php"
const params = `account=${encode(account)}&password=${encode(password)}`

const request = new XMLHttpRequest

request.onreadystatechange = function () {
  if (request.readyState === XMLHttpRequest.DONE && request.status === 200) {
    console.log(request.responseText)
  }
}

request.open('POST', url, true)
request.setRequestHeader('Content-Type', 'application/x-www-url-encoded')
request.send(params)