Finding a license key and authorization code depends on whether you are a legacy user or seeking a new copy. Since SketchUp 2016 is a "sunsetted" version, the process is different than it was at launch. For Legacy License Holders
Trimble no longer sells new perpetual licenses for SketchUp 2016. However, you still have legal options:
Search your inbox for "SketchUp License" or "Trimble." The original email contained both the serial number and the authorization code. sketchup 2016 license key and authorization code
These codes were originally sent via a verification email at the time of purchase or could be retrieved from the SketchUp License Manager . How to Authorize SketchUp 2016
Back in 2016, SketchUp Pro used a two-part credential system to activate the software: SketchUp Pro 2016 Finding a license key and
SketchUp 2016: License Keys, Authorization Codes, and Your Transition Options
Find your confirmation email from when you originally purchased the license. However, you still have legal options: Confirmation Email:
SketchUp 2016 License Key and Authorization Code: A Complete Guide