Consider the following code copied from ACF docs, refactored to work inside a namespace:
add_filter('acf/location/rule_match/user', __NAMESPACE__ . '\acf_location_rule_match_user', 10, 4);
function acf_location_rule_match_user($match, $rule, $options, $field_group)
{
var_dump($options);
wp_die();
}
The problem is, nothing happens. What I confirmed this only occurs when I'm inside a namespace. What am I doing wrong?