Please review the fix provided by Examsoft here,

Application-Service-Unavailable-Mac-Examplify


If you are receiving an error that says Application’s Service unavailable or NATIVE-MSG-SRV-UNAVAILABLE on your Mac, follow one of the two solutions below to fix the error.

Solution 1: Restart
Restart the device. After restarting the device, Examplify should launch successfully.

Note: On slower devices, it may take a minute or two for the application service to start.

Solution 2: Terminal commands
If solution 1 does not fix your issue, then type the following commands into Terminal and restart the device: 
  • sudo launchctl unload /Library/LaunchDaemons/com.examsoft.ExamplifyService.plist
  • sudo launchctl load -w /Library/LaunchDaemons/com.examsoft.ExamplifyService.plist