Filter not working?

I’m trying to use this plugin for the first time. I’m using it with the Catch Everest Pro theme, and trying to list posts from a specific category on a page. I’m using the tag like:
[display-posts category=”openings”] (where “openings” is a category, and there are several posts in the category…)

But all posts (from all categories) are displaying on the page.

I’ve also tried:
[display-posts category_id=”5″] (where “5” is the category ID for the “openings” category)

But all posts are still displaying.

I tried specifying a category that does not exist (just to see if anything different might happen), but it’s still showing all posts.

Am I doing something wrong? Am I missing some key point or detail of the plugin? Is the plugin perhaps incompatible with the Catch Everest Pro theme?

Any help or pointers would be appreciated!