Bukkit

I am having difficulty getting iron nuggets and ingots to work as denominations for currency. 
I have my primary set to emeralds, called "Alaesian Jots," valued at 1. These give me no issues. 
I have diamonds set as "Imperial Astyr"s at value 5, and they give no issues either. 
I also have gold nuggets set as "Saghrel Ba'hn Piece" valued at 3, and they work great. 

I want to use iron nuggets as "Ervyn La'hr Coin"
and iron ingots as "Ervyn Steel Bar" 

But they crash the whole plugin every time I use them at all. 
Even without changing their names, I can't seem to find proper block IDs for using them. 
I've tried inugget, nuggeti, iron_nugget, etc, along with their data ID numbers, but nothing seems to work. 
What's going on? help me please. its such a good plugin otherwise.

hey, idk what update you're using but last time the author worked or talked about this stuff was November 3rd 2017, ...I'm using 1.12.0 and none of my commands work at all, nor can I figure out what material is the currency (probably overlooked it in files) best thing to do is to copy what the console says when it crashes though, goodluck.

Hello mate,

Thank you for the report.

I didn't realize that Minecraft appended a new item with id 'iron_nugget'.

Should you send me a log of your server to be sure what I'm looking for? Thanks.