: For many modern extensions, you activate the license by signing into the Extension Warehouse or the SketchUcation Plugin Store manager with the account used for purchase. Free Alternatives
If you're looking to use SketchUp SubD, here are some steps you can take: Sketchup Subd License Key
Thomas Thomassen is a pillar of the SketchUp community (developing other free tools like QuadFace Tools). Paying for a license supports continued development and updates. How to Install and Activate Your Key : For many modern extensions, you activate the