I created a custom taxonomy in WordPress for article lengths. It's called 'Length' and these are the items within it: image
I also created a custom dimension in Google Analytics (it's index 5), and created a custom Data Layer variable in Google Tag Manager for it. But I think I am referencing the Data Layer Variable Name incorrectly and it is 'undefined' when I preview it in gtm.
I can see the taxonomy 'length' and it's classification 'standard' at the end of the class when I inspect the page, but I can't figure out what the Data Layer Variable Name is (I know I need to use dot notation).
Here's the code that shows when I inspect.
<article id="post-2784" class="post post-2784 type-post status-publish format-standard has-post-thumbnail hentry category-deforestacion category-gran-chaco length-standard">
...
</article>
How do I access the taxonomy correctly for gtm? I'm pretty sure it's just this that is incorrect and spent hours debugging and researching but can't figure it out.