Exclude category

cat_not_in is not a parameter in this shortcode. You can see all the parameters here: https://github.com/billerickson/display-posts-shortcode/blob/master/display-posts-shortcode.php#L40-L85

Also, your wrapper="br" parameter isn’t doing anything. The only available options for wrapper are ul, ol and div.

To get the result you want you’ll need to use a taxonomy query. Change “cat-1” and “cat-2” to the slugs for your two categories. This approach doesn’t accept IDs – only slugs.

This should work:

[display-posts include_excerpt=”true” image_size=”medium” posts_per_page=”30″ taxonomy=”category” tax_term=”cat-1,cat-2″ tax_operator=”NOT IN”]