Its called Token system.
Acme online already using this system.
Its an npc in-game that gives (eps , flowers , maybe gears , items , casual already made in the client)
Well the npc is made in Revo db released by cyber.
But u need a script maybe in ur website to give tokens after donating , u need to learn php coding , java scripts and stuff.
Try this if u want to do it by urself :
