So you want to add someone as an admin on your Reign of Kings server? Well after a bit of time trying to figure it out myself I finally succeeded. It took so long to figure out the correct syntax I thought I better post it in case anyone else is having trouble.

Find the currently empty users section inside your permissions.cfg:

users {
}


For each user add in the following inside the existing user brackets above:

KenMerritt {
groups {
- 'admin'
}
}