Please close the browser and set your primary DNS to google DNS (8.8.8.8), than open a CMD prompt and perform a ipconfig /flushdns
Then restart your services including the Nginx service from services.msc
Try to activate again.
Also disable any antivirus during the activation process and make sure the windows firewall is off
and i have more problem Activation Failed, the message is "license_error.VersionMismatch Mismatching version numbers. Requested 15.0.57336, Actual 15.5.0"