You need to specify the id value that ACF needs to get the field https://www.advancedcustomfields.com/resources/adding-fields-taxonomy-term/
<?php
$categories= get_the_category();
if (!empty($categories)) {
$term_id = $categories[0]->term_id;
$image = get_field('category-image-field', 'term_'.$term_id);
// what you do from here depends on what the field is returning
}
?>