To bypass this, temporarily disconnect your Mac from the internet (turn off Wi-Fi and unplug Ethernet). Open Terminal from the recovery environment or your desktop and manually roll back your system clock to a date closer to Mojave's release, such as September 2019: date 092000002019 Use code with caution.

If you try to run the installer and receive an error stating that the application is "damaged and can't be used," do not panic. This is almost always caused by an expired Apple security certificate embedded in the installer.