add_user_to_blog not working

I have a function that create a new blog and adds a user as an author to that blog. The add_user_to_blog function is not adding the new user to the blog and not giving the author role. any suggestions?

include_once(ABSPATH . 'wp-admin/includes/admin.php');

$user_name = 'furball';
$password = 'password';
$email = 'furball@gmail.com';

$user_id = wpmu_create_user($user_name, $password, $email);

$domain = 'localhost';
$path = '/multisite/hello/';
$title = 'Hello World';
$admin_user_id = 1;

$blog_id = wpmu_create_blog($domain, $path, $title, $admin_user_id, $meta = '', $site_id = 1);

$role = 'author';

$result = add_user_to_blog($blog_id, $user_id, $role);