The File Manager plugin is only available to paid customers, priced at $3 for a monthly license or $50 for a lifetime license (ATOW), available for purchase here.

However you can use the File Manager plugin for free by using the license key 'ILOVEREO' , which was likely enabled by the developers for demo purposes.

You can test the File Manager plugin by adding the line FILEMANAGER_KEY='ILOVEREO' to the end of the VestaCP config file located at /usr/local/vesta/conf/vesta.conf – however this will be disabled and overwritten within a few hours after VestaCP’s update cron executes.

The only way to keep your File Manager active even after a Vesta update is to either have an license server or to install a system cron job to update the VestaCP config after each VestaCP core update. The latter method is significantly easier if you have root access to your server.

In order to create a cron job that will keep the plugin enabled, add the File Manager key to the config file as explained above and then install the following job in the root user’s crontab.

[root@linux ~]# crontab -e

0 */1 * * * /usr/bin/sed -i "/FILEMANAGER_KEY=''/d" /usr/local/vesta/conf/vesta.conf >> /usr/local/vesta/conf/vesta.conf && sudo /usr/bin/grep -q -F "FILEMANAGER_KEY='ILOVEREO'" /usr/local/vesta/conf/vesta.conf || /usr/bin/echo "FILEMANAGER_KEY='ILOVEREO'" >> /usr/local/vesta/conf/vesta.conf

This cron is configured to run hourly and is designed to reset the license key even after it’s removed.

source:  https://blog.perera.io/tech/vestacp-file-manager-free-cron-unlimted/