CMILib is used in multiple plugins as a base core for most used actions like action bar messages, hover over messages, bossbar, material recognition, entity recognitions and so on. Try to always keep this plugin up to date to have best support for most versions out there.
This plugin was fully introduced with 1.17 minecraft version and was set to be required for plugins to work properly.
SpigotMC‘s resource page: https://www.spigotmc.org/resources/cmilib.87610/
Github‘s repository: https://github.com/Zrips/CMILib
Library’s FAQ: https://www.zrips.net/cmilib/faq/