i watched the video which is hard to follow and after numerous attempts i removed the plugin
Very hard to understand how to do it and yes i get the concept and even have chat tell me that i need to put the stuff in the box and when i do and switch power on - nothing happens 

more info would help are you trying to use mode 2 where it will craft mutipal items.

i was trying to emulate what i seen in the video tbh
it needs more of a step by step guide.
its could be a good plugin but i simply could not get it to work 

ok i will try and explain see if it helps..
give your self perm itemprinter.use ,  itemprinter.admin and itemprinter.printer
in the config set

"Mode two": true​

reload the plugin.

For an example lets set it to craft 5.56 Rifle Ammo 

empty your inventory and only place the items you want the printer to use to craft the 5.56 ammo
with just the items in your inventory type in chat command /printer items -1211166256 3

your printers battery must be hooked directly to a switch that has power no other components inbetween the switch and the printer.
you must also know the bp to craft the 5.56
Place one 5.56 amo in the first slot of the box. and anywhere else place in the resorces you had in your inventory when you set in the /printer items turn on the switch.
Please let me know if this helped.

that worked fine - so the issue must of been me not running it in mode 2 
Why is that turned off by default ??

plugin was originaly designed to only craft one custom item and was updated to craft any items.