Sergey Vitalievich, I made the cron work correctly, but you need to do a few things:
1. prescribe in crontab to run cron every half hour
path to ftp/
www/catalog/onebox/cron.phpinstead of the path to ftp you need to put the full path to the directory where opencart is located. There will be something like /var/www/
2. For some of the products of the selected category, in action, put down an additional field that is responsible for uploading goods to opencart.
If suddenly something does not work out, reset the access to your hosting admin panel to the mail so that I can set up the cron personally. Thank you.