when I add another box to geometry and set it to subtractive the entire box including the first one won't appear

[anonymous_user_45e29219]

Hi, I tried to create a simple room for my first project, and yet when I put the box geometry as the first set of wall, it worked. But when I added the second set of wall and set it to subtractive, the entire wall disappears. The room is not there. How do I fix this? I’m new here, hope you can help me.