4th requirement from the end shows an error

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Your code so far

My code satisfied the given requirements. But 4th requirement from the end shows an error. What’s wrong?

<!-- file: index.html -->
<!DOCTYPE html>
<html lang="en">
  
  <head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Technical Documentation Page</title>
    <link rel="stylesheet" href="styles.css">
  </head>
  <body>
    <header>
      <nav id="navbar">
        <header>Navbar Header</header>
        <ul>
          <li><a class="nav-link" href="#Header_Introduction">Introduction</a></li>
          <li><a class="nav-link" href="#Header_Section_1">Section 1</a></li>
          <li><a class="nav-link" href="#Header_Section_2">Section 2</a></li>
          <li><a class="nav-link" href="#Header_Section_3">Section 3</a></li>
          <li><a class="nav-link" href="#Header_Section_4">Section 4</a></li>
          <li><a class="nav-link" href="#Header_Section_5">Section 5</a></li>
        </ul>
      </nav>
      <h1>Technical Documentation</h1>
    </header>
    <main id="main-doc">


      <section id="Header_Introduction" class="main-section">
 <header>Header Introduction</header>       <h2>Introduction</h2>
         
        <p>Welcome to our technical documentation page. This page provides information on our software products and services.</p>
      </section>

      <section class="main-section" id="Header_Section_1">
        <header>Header Section 1</header>
        <h2>Section 1</h2>
        
        <p>This section provides information on our software product.
          <code>var x = 42.</code>
          <code>var x = 42.</code>
          <code>var x = 42.</code>
          <code>var x = 42.</code>
          <code>var x = 42.</code>
        </p>
        <h3>Subsection 1.1</h3>
        <p>This subsection provides detailed information on a specific feature of our software product.</p>
        <h3>Subsection 1.2</h3>
        <p>This subsection provides detailed information on another feature of our software product.</p>
      </section>

      <section class="main-section" id="Header_Section_2">
        <header>Header Section 2</header>
        <h2>Section 2</h2>
        
        <p>This section provides information on our services.</p>
        <h3>Subsection 2.1</h3>
        <p>This subsection provides detailed information on a specific service we offer.</p>
        <h3>Subsection 2.2</h3>
        <p>This subsection provides detailed information on another service we offer.</p>
      </section>

      <section class="main-section" id="Header_Section_3">
       <header>Header Section 3</header> 
        <h2>Section 3</h2>
        
        <p>This section provides information on our company.</p>
        <h3>Subsection 3.1</h3>
        <p>This subsection provides detailed information on our company's history.</p>
        <h3>Subsection 3.2</h3>
        <p>This subsection provides detailed information on our company's mission.</p>
      </section>
      <section class="main-section" id="Header_Section_4">
        <header>Header Section 4</header>
        <h2>Section 4</h2>
        
        <p>This section provides additional resources for our users.</p>
        <ul>
          <li><a href="#">Resource 1</a></li>
          <li><a href="#">Resource 2</a></li>
          <li><a href="#">Resource 3</a></li>
          </ul>

           <section class="main-section" id="Header_Section_5">
             <header>Header Section 5</header>
        <h2>Section 5</h2>
      
        <p>This section provides additional resources for our users.</p>
        <ul>
          <li><a href="#">Resource 1</a></li>
          <li><a href="#">Resource 2</a></li>
          <li><a href="#">Resource 3</a></li>
        </ul>
      </section>
    </main>
  </body>
</html>

/* file: styles.css */
@media only screen and (max-width: 815px) {
  /* For mobile phones: */
  #navbar {
    border: 1px solid;
    height: 207px;
  }
}

Your browser information:

User Agent is: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/111.0.0.0 Safari/537.36

Challenge: Technical Documentation Page - Build a Technical Documentation Page

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I’ve found the issue. thanks!