[Plugin: Simple Custom Post Type Archives] Previous and next link not showing

Hi,

Loving the plugin so far, but the previous and next link in the single pages is not working. Nothing shows up when I put:

<?php next_post_link() ?>

I have 12 posts in that custom post type.

The pagination in the archive for the type is working. I get the newer and and older posts.

Am I doing something wrong?

https://www.ads-software.com/extend/plugins/simple-custom-post-type-archives/