You cannot buy a new license key for 2017 Pro from the official SketchUp store .
Below is an overview of the licensing landscape for 2017, how to handle "fixed" or broken license errors, and legitimate ways to keep using this classic software. Why SketchUp 2017 Pro Licensing is a Challenge
If you own a legitimate 2017 Pro license but are getting errors like "Invalid Serial Number" or "Authorization Failed," try these steps: SketchUp 2017 Checkup
If you bought a license years ago but never "deauthorized" it from an old computer, you may find the system blocks you from activating it on a new one.