You are not running a supported webserver. osTicket does not work with nginx out of the box and requires configuration changes in nginx to work properly. There are a number of threads at github that talk about the configuration changes that you have to make to make it work. You can either read those, and change your config or switch to Apache.

Also CentOS has SELinux enabled by default, and it has also caused some issues with osTicket running properly.

Great glad to hear it. I'll mark this as resolved and close the thread.

Please feel free to start a new thread if you have another question, comment, etc.