Thought to check out what a 3D print from openSCAD would cost.The company can only handle .stl, .3mf, stpThe openSCAD can export to .stl and .3mf (I don't know the difference). When "F5" is pressed - no problems occur. When I select "File" / "Export" / "Export as STL" (F7) The following message is displayed .: "ERROR: Nothing to export! Try rendering first (press F6)" I press "F6" The following message is displayed .:"WARNING: No top level geometry to render" The same thing happens when I try to export to ".3MF" Why / What to do?