I'm currently trying to learn how to use this plugin but I also have an older version of RPG Maker which might be the problem why it's bugging out, yea......
Viewing post in [CGMZ] Crafting for RPG Maker MZ comments
You can download the core from this link which is also in the post under the "Requirements & Terms" heading: https://www.caspergaming.com/plugins/cgmz/core/