Add a purchase interaction to computer

Hi All!

I apologise if this has been answered elsewhere. I haven't really tried much tuning so far, but now I'm trying to add the option to buy an item from the computer.

I've added custom strings to the package and used those in my interaction tuning (extracted this from the purchase medicine option on the computer), but I still don't get the interaction on the computer. For now, I've tried to add the interaction using an override on the Faraday Fizz from JA (I unlocked it so it's buyable from the bb catalog).

Does anyone know where I can find a tutorial for this?  Otherwise, I would appreciate it if anyone can help or steer me in the right direction.

Here's my package file:
drive.google.com/open?id=1AFSAuCjfx3HtYF0XEd4HN2mWlcvJ3I1x