Learn HTML by Building a Cat Photo App - Step 19

Tell us what’s happening:
Describe your issue in detail here.
I follow the steps and instructions in the web page but all failed trying

  **Your code so far**
<html>
<body>
  <h1>CatPhotoApp</h1>
  <main>
    <section>
    <h2>Cat Photos</h2>
      <!-- TODO: Add link to cat photos -->
      <p>Click here to view more <a target="_blank" href="https://freecatphotoapp.com">cat photos</a>.</p>
      <a href="https://freecatphotoapp.com"><img src="https://cdn.freecodecamp.org/curriculum/cat-photo-app/relaxing-cat.jpg" alt="A cute orange cat lying on its back."></a>
    </section>
    <section>
      <h2>Cat Lists</h2>
      <h3>Things cats love:</h3>
        <u1>

        </u1>
    </section>
  </main>
</body>
</html>
  **Your browser information:**

User Agent is: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/103.0.0.0 Safari/537.36

Challenge: Learn HTML by Building a Cat Photo App - Step 19

Link to the challenge:

UL not U1
in lower case