In case you don't have an Internet connection on the Keyserver's computer, you need to follow this process.
Once installed, launch the application Twinmotion Keyserver.
Click on Activate
A dialog appears explaining the process to follow.
Enter your Serial Number (XXXXXX-XXXXXX)
Copy your "Identification Number" given by Twinmotion Keyserver.
Use a computer with an internet connection and go to http://activation.twinmotion.com
Enter the "Identification Number" in the form and click Submit.
The website return a new code you need to use in the field "Manually Activate"
That's it, your Twinmotion Keyserver is now activated.