Fix missing namespace: Symfony\Component\Debug\Exception\FatalThrowableError : Call to undefined function BeyondCode\LaravelWebSockets\HttpApi\Controllers\Psr\str()

src/HttpApi/Controllers/Controller.php

@@ -71,7 +71,7 @@ abstract class Controller implements HttpServerInterface
             'error' => $exception->getMessage()
         ]));
 
-        $connection->send(Psr\str($response));
+        $connection->send(GuzzleHttp\Psr7\str($response));
 
         $connection->close();
     }