Error activating the trial license for PRTG Network Monitor

"System has changed. New activation required. (Failed to establish secure connection Socket Error # 11002)"

PRTG Network Monitor is installed on a Windows 2019 Server Standard. The server is secure so has no access to the internet.

Have tried the offline activation through the Chrome and Firefox Browsers. Have generated the Key a number of times. Have copied the Dat file to the PRTG folder location after stopping the services.

All attempts have failed to activate the license.

Can you advise what I need to do to get the product activated - would like to trial it before purchasing.

activation offline prtg