Warning: include_once(vendor/autoload.php): failed to open stream: No such file or directory in /var/www/html/index.php on line 6

Warning: include_once(): Failed opening 'vendor/autoload.php' for inclusion (include_path='.:/usr/local/lib/php') in /var/www/html/index.php on line 6

Fatal error: Uncaught Error: Class 'App\Site' not found in /var/www/html/config.php:8 Stack trace: #0 /var/www/html/index.php(7): include_once() #1 {main} thrown in /var/www/html/config.php on line 8