Why am I getting this error with laravel websocket library?

am trying to set up a web sockets server using laravel 5.7 and keep getting this error

Argument 2 passed to BeyondCode\LaravelWebSockets\Apps\App::__construct() must be of the type string, null given, called in /opt/lampp/htdocs/api.cs/vendor/beyondcode/laravel-websockets/src/Apps/ConfigAppProvider.php on line 63 screenshot missing

....i don't know what to do please help. I'm actually using this guide https://docs.beyondco.de/laravel-websockets/1.0/

via Chebli Mohamed