For laser cutting, you need a flat DXF containing only the paths you want cut or engraved. A drawing with dimensions, hatching and a title block includes information the machine does not need. Make a separate production version.
Draw at actual size in model space
Work at a scale of 1:1. A line of 100 drawing units should represent 100 mm if you need a 100 mm part. Check the drawing units and export in millimetres. Changing the unit setting alone does not necessarily rescale existing geometry.
Remove additional geometry
Delete dimensions, frames, construction lines, hatching and objects outside the part. Convert any required text to vector outlines. Check block contents too: a block can contain additional paths that are hard to see in normal view.
AutoCAD's OVERKILL command can clean up duplicate or overlapping lines, arcs and polylines. Review its settings carefully; different colours may represent different operations. Save a copy first and compare the result.
Save the production version as DXF
Select DXF when saving or exporting. Area engraving requires closed shapes. Close a contour by actually connecting its endpoints, rather than zooming out until the gap becomes invisible.
Compare a known dimension
Reopen the DXF and measure the overall width or the distance between two holes. Check the same dimension after uploading. A consistent scaling factor often indicates a unit or scale mismatch; preferably fix it in the source file.
Use the drawing guidelines for colours, text and spacing. If shapes are missing after upload, see help with ordering online.