My first idea (I’m not sure it’s the most efficient) is to do a redirection in the file category.php
or archive.php
depending of your theme.
Try with this code before the get_header()
line :
$term = get_queried_object();
if ( ("category" === $term->taxonomy)
&& (0 !== $term->parent) // if it's not a 1st level category
) {
// get the parent
$parent = get_term($term->parent);
// redirection
$url = get_term_link($parent) . "#" . $term->slug;
wp_redirect($url);
exit();
}
this code only work with a 2 levels taxonomy because the redirection ends at the 1st level.