Starting with SketchUp 2021, Trimble (the developer of SketchUp) transitioned from perpetual "Classic" licenses—which used serial numbers—to a subscription model SketchUp Community No Codes Required:

Only users who still hold an older "Classic License" (purchased before the subscription shift) use serial numbers. However, these are generally not compatible with the 2023 version unless specifically converted or maintained through a maintenance plan. How to Activate Your Official Copy

If you have a valid subscription, follow these steps to activate SketchUp Pro 2023: Activating SketchUp Pro

For SketchUp Pro 2023, you do not need a serial number or authorization code for standard activation. Trimble ID: Your license is tied directly to your email address . To activate, you simply sign in with your Trimble ID inside the application. Classic Exception:

SketchUp Pro 2023 , the concept of a "Serial Number" and "Authorization Code" has largely been replaced by a modern subscription-based system. If you are looking for these codes to activate your software, the process has changed significantly from older "Classic" versions. SketchUp Community The Shift from Serial Numbers to Trimble IDs