You have osTicket set to use PHPMail not SMTP. This could be a problem with osTicket sending emails.
As far as receiving emails you haven't show me your email settings for the account that is used to collect email.
As far as your cron
Jurel re cron, i have edited the file from /etc/crontab and added this line.
*/2 * * * * /usr/bin/php -q /var/www/osticket/upload/api/cron.php
Some cron's require the user specified I do not know if your system requires the user to execute it as, but it should be the same user that your web site runs as.
-q is pretty deprecated. Running PHP at command line shouldn't required this directive.
What version of PHP is at /usr/bin/php? (at a command prompt type
/usr/bin/php -v and hit enter)
If you have multiple versions of PHP installed this might not be the same version that your web site is running as (7.2.24)