Ensure your firewall isn't blocking SketchUp's ability to ping the activation server.
There are several ways to obtain a SketchUp Pro 2019 serial number and authorization code: Sketchup Pro 2019 Serial Number And Authorization Code List
If you've purchased SketchUp Pro 2019, your serial number and authorization code can be found in the following locations: Ensure your firewall isn't blocking SketchUp's ability to