Please install Sketchucation Tools: https://sketchucation.com/plugin/696-sketchucationtools

Restart SketchUp after installation

Then license Curviloft per the licensing guide: https://downloads.sketchucation.com/licensing/SCFLicense-Instructions_to_Users.pdf

You can retrieve your license at https://sketchucation.com/webshop/my-licences.php

Curviloft require Libfredo v14.5: https://sketchucation.com/pluginstore?pln=LibFredo6

Try that and report any errors if you encounter them