Autocad - Filletedge a Box

I am just starting in Autocad 2018, under 3D Basics tools.

I have created a BOX, and then I am trying to apply the FILLETEDGE command, and after selecting any edge, the message "No fillet to be computed" results, since I cannot select any edge, nor any fillet is displayed as preview when hovering over any box edge, though the edges highlight when hovered over. The radius is already set to a proper value (Edge: 50, Radius: 3). X-Ray Visual Style do shows the box in blue-grey transparency.

Should I made some previous conversion on the BOX (which I understand already is a 3D Solid) object for the FILLETEDGE command (which too should work on 3D Solids?) to work?