Drupal 7 #ajax callback on form submit
You haven't actually wrapped the element, you've inserted an empty &lt;div&gt; immediately before it.

You need to use #prefix and #suffix to wrap an element in HTML:

...
'#prefix' =&gt; '&lt;div id="replace_hotelbook_div"&gt;',
'#suffix' =&gt; '&lt;/div&gt;'