1) Before you import this plugin in your plugins folder make sure that you have downloaded multiverse core and multiverse inventories plugin.
2) Also create a world named "LOBBY" using the following command in-game:
/mv create LOBBY normal -t flat (or) default
3) After following step 1 & 2 import this plugin in your plugins folder and restart your server then this plugin will work.
4)Since this plugin is admin-proof make sure that you have created the lobby because once you import this plugin you won't able to place or break blocks in lobby world.
Note: This plugin only works in world that you named as LOBBY.