Railgun should be installed and setup separately from the cPanel plugin for Cloudflare.
First make sure you have installed Railgun. Installation instructions can be found here.
Once you installed and activated Railgun on your server(s) you have two options to make it available to your customers:
- Using IPs: Add IP addresses or range of IPs. Once you done this step, under "Performance" settings of cPanel Cloudflare plugin your customers will be able to see railgun and enable it on their domain.
- Adding individual domains: Add the specified domains and associate them with appropriate Railgun. This will enable railgun for those domains - which means no action is necessary then in cPanel.