Exclude category from related posts

Hi,

I’ve tried to exclude one of my categories named “portfolio” from related posts, following the instructions:

function jetpackme_filter_exclude_category( $filters ) {
$filters[] = array( ‘not’ =>
array( ‘term’ => array( ‘category.slug’ => ‘portfolio’ ) )
);
return $filters;
}
add_filter( ‘jetpack_relatedposts_filter_filters’, ‘jetpackme_filter_exclude_category’ );

Yet the posts from this category keep on showing up in the related posts section.

Any idea how to fix this?

Thank you for your help!