First of all, this is the first version of the plugin, we plan to add a in-game help command on future!
The color code system is "Overengineered" because it's meant to support 1.16, and 1.16 supports RGB colors.
Your placeholder is wrong, the correct one is %luckperms_prefix% AND it needs the LuckPerms extension to be installed (you can do it by using /papi ecloud download LuckPerms and /papi reload)
If you need any help, feel free to ask on our discord!