I got a valid license (serial number + authorization code) bought in 2018 for Sketchup Pro 2015 and succesfully installed on my previous PC. I uninstalled it to be able to install it on my new PC. However, when prompted to SN and auth code, I enter them and click on the Add License button, but nothing happens.
I also retrieved a License.sl file in my archives, but don’t know if it is useful.