Unable to download Mojave for upgrade
I'm trying to upgrade iMac to Mojave from Sierra (have an essential app that's incompatible with Catalina). When I try to download Mojave from App Store, I get error "This copy of the Install macOS Mojave.app application is damaged, and can‘t be used to install macOS" and cannot even download it. Any idea how to fix? Thanks.
iMac 27", macOS 10.12