Negative meta_query if storing multiple post_meta values with shared meta_key
Thats because you created the meta_query property incorrectly, it should be a multi diminsional array. $pet_owners = new WP_Query([ ‘post_type’ => ‘pet_owner’, ‘posts_per_page’ => -1, ‘meta_query’ => [ [ ‘key’ => ‘pet’, ‘value’ => ‘cat’, ‘compare’ => ‘!=’ ] ] ]); For more information about meta_query see Custom Field (post meta) Parameters