I can't add more items

Free version has limitations, one of them is the amount of items you can create, which is 25 items, if you installed the plugin, started to create some items, and after a couple of them you got an error message saying :

It is because the amount of items register the item you created and the default items the plugin has, so, if you aren't using some of the default items, just delete them and your amount of items available will increase.

If want them to come back, just use /ei default_items