Hi @klevermedia
You can’t echo the_sub_field() function as it already echoing it’s value by itself. Also, you can’t echo a Taxonomy field because it is an object, not a string. I think you can do it like this:
$theTerms = get_sub_field('category_button_url');
echo get_term_link( $theTerms );
This page should give you more idea about it: http://www.advancedcustomfields.com/resources/taxonomy/.
I hope this helps.
