- Edited
The rcron.php file is in the download archive that you downloaded to get osTicket.
Docs are
https://docs.osticket.com/en/latest/Getting%20Started/POP3-IMAP%20Settings.html
and there are some comments in the file. Additional comments can be found using search such as in these threads:
https://forum.osticket.com/d/96721-using-api-rcron-php-and-api-ticket-create-php
https://forum.osticket.com/d/79232-how-to-set-up-remote-cron-rcron