The error shows the application cannot communicate with our server to perform activation. This could be a firewall issue with your network. Can you check the following requirements with your IT department?
Alternatively, you can connect your Newline screen to a mobile hotspot (from your phone) and try to activate it once more. Here are guides to activate a mobile hotspot:
This turns your phone into a separate Wi-Fi option from your network. From here, you can connect your Newline display to the hotspot the same way you would connect any device to a Wi-Fi network. Then you can activate the Key/proceed with activation.