I followed the instructions and reread them. I entered the shop and got shown this error.

Error running script: Error compiling expression 'obj.alias + " (" + DisplayMoney(BuyingPrice(obj)) + ")"': Value cannot be null.Parameter name: key

I have no idea what is causing the issue. I am new to this and am learning.

So after a bit of rereading, I forgot to set two of the required scripts to integer return type. My bad.