live.ERROR：“cron”命名空间中没有定义命令

I have been trying to set up crontab on a Plesk server with Laravel 5.8, and I am getting the following error:

live.ERROR: There are no commands defined in the "cron" namespace. {"exception":"[object] (Symfony\Component\Console\Exception\NamespaceNotFoundException(code: 0): There are no commands defined in the \"cron\" namespace. at /var/www/vhosts/****************/httpdocs/vendor/symfony/console/Application.php:585)

I have tried:

cd /var/www/vhosts/**********/httpdocs && php artisan schedule:run >> /dev/null 2>&1

php /var/www/vhosts/**********/httpdocs && php artisan schedule:run >> /dev/null 2>&1

The code in kernel.php is:

$schedule->command('command:videos')
         ->everyFifteenMinutes()
         ->timezone('Europe/London');

The problem is in kernel.php. The command needs to be:

$schedule->command('cron:videos')
         ->everyFifteenMinutes()
         ->timezone('Europe/London');