IMPORTANT: The laser cutter cares not for fills and shades. it just reads the lines. So let’s get rid of the colour fill and give the shape an outline instead.
Select the rectangle and then, if the fill and stroke box isn’t already open on the right hand side of the screen, click the little double arrow in the bottom corner and select fill and stroke to open the window.
In this window you have 3 tabs – Fill, Stroke paint, Stroke style.
With the fill tab selected, click the X to remove the fill colour from the shape.
Now select the Stroke paint tab and choose the first filled square. This will open another area for you to choose the colour you want to use for the outline. You can leave it black for now.