Assigns a subscriber to a certain list if a certain link has been clicked

Add user to list after click on link

function my_add_user_to_list_after_click_on_link (  $subscriber_id, $campaign_id, $target, $index ){
    
    $link = 'http://example.com';
    $list_id = 123;
    $remove_from_old_lists = false;
    
    if( $link == $target ){
    
        mailster('subscribers')->assign_lists($subscriber_id, $list_id, $remove_from_old_lists);
    
    }
    
}

add_action( 'mailster_click', 'my_add_user_to_list_after_click_on_link', 10, 4);

Your code don't work for my.
I tested with the following code for cancel subscripton for list 1 and suscribe to list 2 if the user click a button:

add_action('wp_head','mymail_change_list_segment');
function mymail_change_list_segment() {
if ( is_page(711) ) {
$userhash = isset($_COOKIE['mymail']) ? $_COOKIE['mymail'] : NULL;
$subscriber = mymail('subscribers')->get_by_hash($userhash, true);
$user_mail = $subscriber->email;
$lists = 1;
global $user_mail, $userhash, $lists, $subscriber;
$subscriber_ids = mymail('subscribers')->add(array(
'email' => $user_mail,
'status' => 1,
), $overwrite = true );
mymail('subscribers')->assign_lists($subscriber_ids, $lists, $remove_old = true);
}}