Fatal error: Uncaught Error: Interface "Ratchet\WebSocket\WsServerInterface" not found in /var/www/html/lib/Ratchet/src/Ratchet/Wamp/TopicManager.php:6 Stack trace: #0 {main} thrown in /var/www/html/lib/Ratchet/src/Ratchet/Wamp/TopicManager.php on line 6