Hi Sayuri!
Yes, the $login_url param is a string, so you should also return a string.
It will depend on where your login page is located, but here’s a sample code for you to try:
add_filter( 'tribe_tickets_ticket_login_url', 'custom_tribe_tickets_ticket_login_url' );
function custom_tribe_tickets_ticket_login_url ( $login_url ) {
// return the permalink to post id = 2
$login_url = get_permalink( 2 );
return $login_url;
}
You can place that into your theme’s functions.php file.
Does it help?
Best,
Victor