JSON APIs and AJAX code passes, but browser doesn't show result on click

So exactly as the title. I have already passed these challenges, but it’s eating me up inside that I’m not seeing the results I want on the browser. Not sure what’s wrong.

<script>
  document.addEventListener('DOMContentLoaded',function(){
    document.getElementById('getMessage').onclick=function(){
      // Add your code below this line
req = new XMLHttpRequest();
req.open('GET', '/json/cats.json', true);
req.send();
req.onload=function(){
  json=JSON.parse(req.responseText);
  document.getElementsByClassName('message')[0].innerHTML = JSON.stringify(json)
}

      // Add your code above this line
    };
  });
</script>
<style>
  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;
  }
</style>
<h1>Cat Photo Finder</h1>
<p class="message">
  The message will go here
</p>
<p>
  <button id="getMessage">
    Get Message
  </button>
</p>

I just checked the console:

I pass the challenge: