title: Multiple GPT ads in same page display only once
body: <p>i need display multiple ads on one page with this code:</p>
  <pre><code>&lt;script async src=&quot;https://securepubads.g.doubleclick.net/tag/js/gpt.js&quot;&gt;&lt;/script&gt;
  &lt;div id=&quot;gpt-passback650x250&quot;&gt;
  &lt;script&gt;
  window.googletag = window.googletag || {cmd: []};
  googletag.cmd.push(function() {
  googletag.defineSlot('/162717810/xxxxx/650x250', [650, 250], 'gpt- 
  passback650x250').addService(googletag.pubads());
  googletag.enableServices();
  googletag.display('gpt-passback650x250');
  });
  &lt;/script&gt;
  &lt;/div&gt;
  </code></pre>
  <p>If i use this code twice or more on page, i get error: <strong>Exception in queued GPT command TypeError: Cannot read property 'addService' of null</strong></p>
  <p>Code must be same, customer want paste it to page via shortcode in cms. How to solve this? Thanks</p>