First, make sure that the spacedesk Driver is properly installed and can be seen in Windows Control Panel's  Programs and Features.




Check if the spacedesk System Tray icon (at the bottom right of the screen) is visible in the notification area and click it to show spacedesk status ON in spacedesk Driver Console app.



       




Check the Windows Firewall settings if spacedeskService.exe is allowed on private or public network. 
Open Control Panel → Windows Firewall → Allow an app through Windows Firewall, allow an another app then browse for spacedeskService.exe located at “C:\Windows\System32” folder.