TimedPermissions/kits
So basically I want to add a timedpermission to a kit. I want the user to purchase the kit using server rewards. When purchased, I want them to be added to a user group, for example VIP user group. I can't figure it out. Could anybody give me a guide on how to do this. I'm using carbon.

Using a files to save and load data of player that used Server rewards!

That doesn't make any sense to me. Sorry. 

I use PlayerRankings@Ankawi and PlaytimeTracker with kits (and other plugins) to give rewards to players for staying on the server, the ranks are based on hours and each rank (over basic amount of time) can obtain a kit permission (or plugin permission like backpacks slots) , it is not exactly want you want but it might give  you some ideas.

Thanks for the suggestion. I really want them to be added to a group to receive VIP benefits. Can not seem to find any help anywhere.

Use the hooks in kits and in timed permisions. and make the plugin