Hi @hambos22
Unfortunately, you need to set the second parameter with the taxonomy name and the term ID like this:
get_field('us_' . $productBrandSlug[0], 'taxonomy-name_99');
Where 99 is the ID of the term. This page should give you more idea about it: https://www.advancedcustomfields.com/resources/get-values-from-a-taxonomy-term/. Maybe you can use the get_term_by() function.
I hope this helps.