Thank you @aisyaastari !!! This is the information we’ve all been interested in.
As @Douglas pointed out, in the Layout mode even if there’s not a seam allowance it still exports the cutline on top of the seamline, which creates problems.
So one more parameter is needed: Check the Seamline ‘Built in’ option so that the seamline becomes the cutline with no seam allowance.
Summary to export to CLO3D:
In Seamly2D:
Set pattern piece seam allowance with checkbox ‘Built In’
Export as “DXF R10 AAMA”
In CLO3D:
Import with “Auto-trace as Internal Lines” and “Optimize All Curve Points”
And something for me to look into is improving the “Toggle Allowance” toolbutton to act as a global built-in SA in Piece and Layout mode vs just hiding the SA in the Piece mode display. That way a user can export all the pieces with or without the SA simply by toggling the toolbutton… OR maybe (also) adding an “Export with SA” option to the export? Or for that matter add a check list of what parts to include in an export… SA, Grainline, Labels, Notches, etc. This would probably make life easier for anyone exporting multiple sizes that they then make into a nest in another app like Inkscape. Hmmm.