Calendar not syncing iMac, iPhone and iPad
I can't get my Mac Calendar to sync on iMac Late 2009 (High Sierra 10.13.6) to My iPad Pro (iOS 12.3.1) to My iPhone SE (iOS 12.3.1) They all on iCloud with the correct user name. I've searched and followed instructions but cant get it right. Perhaps the MacOS is too old? Any suggestions would be appreciated.
iMac 27", macOS 10.13