Fatal error: Uncaught Error: Call to undefined function Cornerstone\API\ThemeOptions\add_filter() in /home/frassati/public_html/wp-content/plugins/cornerstone/includes/integration/Api/ApiThemeOptions.php:36 Stack trace: #0 {main} thrown in /home/frassati/public_html/wp-content/plugins/cornerstone/includes/integration/Api/ApiThemeOptions.php on line 36