We're you standing in the dirt or on the green? I set the collision up so that you need to be standing on the dirt patch of where you want to plant when you press 'E'.
Also after I implemented a shader on all the interactables I did notice there was a small hiccup in my web build the first time you plant something but I haven't had a minute to get to a computer where I can use a debugger to see what's going on on the web build.
One thing I plan to add after the jam is for NPCs toll give you a "you are out of pumpkins" message if you try to sell them pumpkins and you don't have any.