Hello there.
I have sent you a DM on discord, but it won't send because we don't currently have any servers in common. My discord handle is @capnrammo. I'm sure I posted it... somewhere on here.
Anyways, the good news is that I'm pretty sure I know what the problem here is.
Your first issue with the crash on the item scene is because the plugin parameter "Updated Scene Item" from ItemCore is true and it should be false. That parameter makes ItemCore redraw the item scene in a fancy way in MV, but in MZ this breaks the whole scene because it was never intended to be used in MZ. Because of that, the independent item patch doesn't touch any of those windows the updated scene tries to draw, so it throws that error when it tries to draw a window in the old MV way. Disable that parameter in the demo and it will stop doing that.
Near as I can tell, every other problem you're having is because of the demo project. The demo project works out of the box, without modification. If you redownload it, extract it, open it in MZ and run it, you can craft any of the recipes included without issue. The problem is that the demo project was intended only to ever be used with version 1.00 of the original plugin, which it includes already. Since that release, I split the plugin into the core and the MZ/MV versions, and the demo doesn't work with that. So if you update any of the plugin files in the demo, you need to do a bunch of troubleshooting to get it to work again.
The demo is more for seeing how it should be set up, so you can compare it with your own project as you make your own recipes. If you import the newer versions directly into your project, they will grab the default plugin parameters and should work just fine, but the demo version already has parameters setup for the plugin, so it doesn't reset to defaults, and gets a little messed up. One way to check this is that in the plugin params for the bug project you uploaded, there are no recipes listed at all.
However, even after adding one, it still can't be crafted and returns a total failure, as you said. On the other hand, all recipes in the unmodified demo project worked fine, and making the same recipes in a brand new project with the updated plugins also works fine (although setting it up takes quite a bit of work).
As for refunds, itch does allow you to refund your purchases, and I have no personal problem with refunding a plugin you can't make use of, or that doesn't work the way you wanted it to, after all, it's hard to know exactly what you're going to get when you buy something like this. But at this point, the problem is purely configuration, and it can definitely work. Many people have purchased, used, and even modified this plugin to great effect, and I'm sure you can get it to work too.
~Ramza
