rfa to iges conversion is pretty much certainly related to export of Revit architecture content (.rfa files) to IGES format (.igs or .iges), which is unfortunately not a straightforward process, because of the difference of data.
The usual work around is to export your .rfa to OBJ format via OBJ Exporter for Revit and export the OBJ file to IGES format instead, using any of the available obj to iges converters.
Updated: October 10, 2023