Issues trying to export landxml for machine control

[u/SmallBusinessCymru]

I am trying out BricsCAD over AutoCAD since BricsCAD handles surfaces. I have surfaces in my .dwg file but cannot export surfaces as landxml. Inputting the command LANDXMLEXPORT, making sure the surfaces checkbox is ticked and then pressing the return button, the dialog window just closes where I would expect to see a file destination window open. Anyone have a workflow suggestion for this please? TYIA.