Dragging a card to player hand

I’m developing a game module (I’m new with Vassal) but I’m not able to drag a card from Map window deck to a player hand window. The dragged card goes always down to the main board, so seems that nothing can be dragged on a Player Hand window.
does anyone any idea of what can happen?

Is it possible that you’re running the module currently as “” rather than as one of the players who “owns” the hand?

I also tried chosen a player side but happens the same. It doesn’t matter, I’ll use Map window instead. thanks.