$args = array(
            'post_type' => 'produkt_varianten',
            'posts_per_page' => -1,
            'fields' => 'ids',
            'meta_query' => array(
                array(
                    'key' => 'a001',
                    'value' => $groupNameArray,
                    'compare' => 'IN'
                )
            )
        );