Fatal error: Uncaught Error: Class "APP\handler\Handler" not found in C:\xampp\htdocs\ojs\lib\pkp\controllers\api\file\PKPManageFileApiHandler.php:39 Stack trace: #0 {main} thrown in C:\xampp\htdocs\ojs\lib\pkp\controllers\api\file\PKPManageFileApiHandler.php on line 39