title: do_shortcode: Opening and Closing tag with variable inside between quotes
body: <p>can you help me fix this code?
  It's supposed to get the Product ID (which it does), then get the Custom Field called "ID_del_curso" (which it does), and finally, print out a shortcode [student course_id="$courseid"]HTML[/student]</p>
  
  <p>The button is displaying for anyone who accesses the site, not just the people who qualify as a student of the Course number embedded inside the Product.</p>
  
  <p>I'm guessing the error is where the "echo" line is... I'm going crazy over here! Help!!! Thanks so much :D</p>
  
  <pre><code>&lt;?php
      global $product;
      $postid = $product-&gt;get_id();
      $courseid = get_post_meta( $product-&gt;get_id(), 'ID_del_curso', true );
      $html = '&lt;center&gt;&lt;div class="alreadyPurchased"&gt;&lt;i class="fas fa-graduation-cap paddingRightM"&gt;&lt;/i&gt; Ya te has registrado&lt;/div&gt;&lt;/center&gt;';
      echo do_shortcode("[student course_id=&amp;quot;" .$courseid. "&amp;quot;]". $html . "[/student]"); 
  ?&gt;
  </code></pre>