Upgrade from High Sierra to Mojave on late 2013 imac
I'm trying to upgrade to OS Mojave from High Sierra (10.13.6) on my late 2013 27" i Mac. When I'm directed to the app store, the version of OS says it is damaged and can't be installed. Is there another source for OS 10.14.6? Am I too late to upgrade? Thanks
iMac 27″, macOS 10.13