No se que pasa en el ultimo input


<h2>CatPhotoApp</h2>
<main>
<p>Click here to view more <a href="#">cat photos</a>.</p>

<a href="#"><img src="https://cdn.freecodecamp.org/curriculum/cat-photo-app/relaxing-cat.jpg" alt="A cute orange cat lying on its back."></a>

<p>Things cats love:</p>
<ul>
  <li>cat nip</li>
  <li>laser pointers</li>
  <li>lasagna</li>
</ul>
<p>Top 3 things cats hate:</p>
<ol>
  <li>flea treatment</li>
  <li>thunder</li>
  <li>other cats</li>
</ol>
<form action="https://www.freecatphotoapp.com/submit-cat-photo">
  <input type="text" placeholder="cat photo URL">
  <button type="submit">Submit</button>
*<input type="text" required>*
En esta parte no se que pasa, no me deja 
</form>
</main>

Hola,
Agregue la dirección web del tutorial, Por favor.