Ultimate Member plugin hooks are not working

I am trying to use the Ultimate Member plugin's hooks, but I can't get them to work.

Here is my test code:

add_action( 'um_user_register', 'my_user_register', 10, 2 ); function my_user_register( ) { die('from codex'); }

But when I register a test user from UM's registration form, my_user_register() does not execute. Am I doing something wrong here, or is there a problem with the Ultimate Member plugin?

EDIT: I forgot to add that the above code is in my wordpress theme's functions.php file.