How can I retrieve the slug for a custom post type via name?

I found an alternative solution: get_post_type_archive_link( $post_type );

Instead of providing a slug, it retrieves the archive url for a designated custom post type.

e.g.

<a href="https://wordpress.stackexchange.com/questions/124559/<?php echo get_post_type_archive_link("books' ); ?>">Movies Archive</a>