Your device has an internet connection, but you get an error message indicating that activation cannot be completed. Security features in Windows operating systems (especially since Windows 10), and virus protection applications in general, can sometimes interfere. To allow ExtendSim through the firewall:
Go to Settings > Update & Security > Windows Security (on left hand side).
Under Protection Areas, select Firewall & Network Protection and Allow an app through the firewall.
Then click the Change Settings and Allow another app buttons.
Browse to ExtendSim 10 and click Open. In the dialog that appears, click Add.
Try activating ExtendSim again.
If automatic activation isn't allowed, the error message has instructions for performing a manual activation.