Fatal error: Uncaught Error: Class "PKP\mail\Mailable" not found in /var/www/html/lib/pkp/classes/mail/mailables/DiscussionCopyediting.php:28 Stack trace: #0 {main} thrown in /var/www/html/lib/pkp/classes/mail/mailables/DiscussionCopyediting.php on line 28