Hi! Thank you for asking before reviewing! Means alot! Currently in the build it's less of a "open shop" and more that you can sell from. Your bag whenever you stand by the box.
So it should (unless it's a bug and there are sadly some) be enough to go up to the box -> open your bag with "B" -> beside each fish there should now be a moneybag icon that you can click (as long as you stand near the chest that will be highlighted) and get the money!
Sorry if it's a bit hard. If there was more time I planed to make a seperate ahop but ran out of time. 😅
But hope that helps and thank you for playing and caring enough to ask ❤️