Can't pass the test, code seems to do what it should do

So this happens quite often to me. The test should give a pass but instead I get some exceptions… In this case I got back :

Your code should get the element with class message and change its textContent to “userName loves cats”

it does that.

Your code should use the send method.

I used the send method.

P.S this wasn’t the original code I changed it as close to the example as possible just to let the code pass.

Your code so far

document.addEventListener('DOMContentLoaded', function(){
  document.getElementById('sendMessage').onclick = function(){

    const userName = document.getElementById('name').value;
    const url = '';
    // Add your code below this line

    const xhr = new XMLHttpRequest();'POST', url, true)
    xhr.setRequestHeader('Content-Type', 'application/json; charset=UTF-8')
    xhr.onreadystatechange = function () {
      if (xhr.readyState === 4 && xhr.status === 201){
        const resp = JSON.parse(xhr.response)
        document.getElementsByClassName('message')[0].textContent = resp.userName + " loves cats"
     xhr.send(JSON.stringify({ userName: userName })) 
    // Add your code above this line

body {
  text-align: center;
  font-family: "Helvetica", sans-serif;
h1 {
  font-size: 2em;
  font-weight: bold;
.box {
  border-radius: 5px;
  background-color: #eee;
  padding: 20px 5px;
button {
  color: white;
  background-color: #4791d0;
  border-radius: 5px;
  border: 1px solid #4791d0;
  padding: 5px 10px 8px 10px;
button:hover {
  background-color: #0F5897;
  border: 1px solid #0F5897;

<h1>Cat Friends</h1>
<p class="message box">
Reply from Server will be here
<label for="name">Your name:
  <input type="text" id="name"/>
<button id="sendMessage">
  Send Message

Your browser information:

User Agent is: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Firefox/78.0.

Challenge: Post Data with the JavaScript XMLHttpRequest Method

Link to the challenge: