The tag tells MCU how to install a mod once it has been downloaded. This is a required tag. There are currently 8 different valid types, but for modern packs, you usually only need to consider these first three:
The links above will take you to the CurseForge page for the Iron Chests Mod. Specifically, they direct you to the download for your chosen version of Minecraft. Learn more about why you should only download files from CurseForge.
If you update a config file, you can use /gpreload to reload the config. This does NOT completely reload the plugin, so if you download an updated JAR file, you still have to /reload or reboot your server to get all the changes. 781b155fdc