Fatal error: Uncaught Error: Interface 'Ratchet\Session\Serialize\HandlerInterface' not found in /home/soh-works/www/websoket-sample/vendor/cboden/ratchet/src/Ratchet/Session/Serialize/PhpHandler.php:4 Stack trace: #0 {main} thrown in /home/soh-works/www/websoket-sample/vendor/cboden/ratchet/src/Ratchet/Session/Serialize/PhpHandler.php on line 4