Post category on masonry shortcode

Hi there,
I’ve tried adding the following code to my functions.php to display the category in the masonry blog posts but it isn’t showing up.

add_filter( 'avf_masonry_loop_prepare', 'avf_masonry_loop_prepare_mod', 10, 2 );
function avf_masonry_loop_prepare_mod( $key, $entries )
{              
	$class = preg_grep('/category/', $key['class']); 
    $getstr = str_replace('category-', '', implode(',', $class)); 
	$categories = explode(',', $getstr);
	$cat = implode(',', array_map('ucfirst', $categories));	
	foreach ( $key as $post => $value ) {
			if ( $post == 'content' ) { $value .= "<div class='av-masonry-categories'>".$cat."</div>"; }
			$key[$post] = $value;
	}
   

Thank you