Google SDTT error: "The review has no reviewed item specified."
<p>I checked my website's Rich Snippets in the Google Rich Snippets Tool, and it had an error:</p>

<blockquote>
  <p>The review has no reviewed item specified.</p>
  
  <p><img src="https://i.stack.imgur.com/3nURL.png" alt="Picture of the error Google shows"></p>
</blockquote>

<p>How do I fix it? </p>

<p>The code is:</p>

<pre><code>&lt;div itemprop="aggregateRating" itemscope="" itemtype="http://schema.org/AggregateRating"&gt;
  &lt;span itemprop="ratingValue"&gt;5&lt;/span&gt; stars - based on &lt;span itemprop="reviewCount"&gt;21&lt;/span&gt; reviews
&lt;/div&gt;
</code></pre>