Custom Model with Image Upload section

Hello Everyone,
I’m trying to set up a panel in which you can add items(products) from Neos’ backend, and in certain pages I’d like to show said products and their attributes, but as I try to upload an Image (pic 1) I get this error (pic 2) and I was wondering if anybody could give me a hand, trying to figure out what’s it about and maybe some fixes. I’ve tried to look into converters but I can’t fully grasp how they work.