I am also experiencing the same issue. I also bought the “EZkeys Small Upright Piano” during the black friday sale. If I try to purchase Now I wanted to purchase an Addon, the button is greyed out and it says “REQUIRED PRODUCTS”, but among those in the list is “EZkeys Small Upright Piano – Regular”. I tried different browsers, cleared cookies, and logged out and back in but the button remains greyed out for me.
