Update: I managed to complete the installation by killing all processes on port 80, however, I have no idea if this is a long-term fix (presumably not).
Mac:
# find & kill processes which are using port 80
sudo lsof -i tcp:80 | grep LISTEN | awk '{print $2}' | xargs kill -9
Windows:
# find processes which are using port 80
netstat -ano | findstr :80
# kill process by PID. replace "<PID>" with result from the above command.
taskkill /PID <PID> /F
Support: DevKinsta Error Codes - Kinsta
Best,