[image-intro-url] not working

<div id="services" class="text-center">{articles category="8"}
  <div class="service card">
    {if image-intro}
      <img src="[image-intro-url]" alt="[title]" />
    {else}
      <img src="https://dummyimage.com/160x160/ebebeb/373f50.jpg" alt="[title]" />
    {/if}
  <h3 class="h4">[title]</h3>
    [text]
  </div>
{/articles}