Hello Hernan,
Thank you for reaching out! You can configure yourself native PHP and write something from alt-PHP there. This document will also help you
https://docs.cloudlinux.com/cloudlinux_os_components/#configuration-and-using.
It is also possible that the file is incorrectly configured: /etc/cl.selector/native.conf
Check the settings please:
php=/usr/bin/php-cgi
php-cli=/usr/bin/php
php.ini=/etc/php.ini
php-fpm=/usr/sbin/php-fpm
Let me know if you need anything else. Thank you!