You can find instructions on setting up the vnStat PHP web interface on CentOS and Fedora in a tutorial published by TecAdmin.

Setting Up vnStat PHP Web Interface on CentOS and Fedora

vnStat is a lightweight, command-line network traffic monitor that allows you to track the bandwidth usage of your network interface. While it’s easy to use, it might not be the most user-friendly option for everyone. That’s where the vnStat PHP web interface comes in – it provides a graphical representation of the network traffic data

Setting Up vnStat PHP Web Interface on CentOS and Fedora – TecAdmin