error datos estructurados

//add hatom data extra

function add_suf_hatom_data($content) {
 $t = get_the_modified_time('F jS, Y');
 $author = get_the_author();
 $title = get_the_title();
if (is_home() || is_singular() || is_archive() ) {
 $content .= '<div class="hatom-extra" style="display:none;visibility:hidden;"><span class="entry-title">'.$title.'</span> was last modified: <span class="updated"> '.$t.'</span> by <span class="author vcard"><span class="fn">'.$author.'</span></span></div>';
 }
 return $content;
 }
add_filter('the_content', 'add_suf_hatom_data');