Your GLPI server must be able to reach services.glpi-network.com to validate the key.
If your GLPI registration key doesn't seem to work, check the following: glpi registration key work
Ensure your web server has the correct permissions to write to the configuration directory. Your GLPI server must be able to reach services
You can obtain a key even if you are using the free community version of GLPI. glpi registration key work
Are you planning to use the for specific plugins, or are you looking into professional support for a large-scale deployment? Registration key marketplace | Tutorials | Help Center GLPI
Visit the GLPI Network registration page and create an account.