Unable to download macos Mojave

The error message is misleading, what it should actually say is the App Store has detected a copy of

Install macOS Mojave.app in your Applications folder. Locate it, move it to the Trash, empty the Trash.

Connect your mac to your router via cable, Restart your mac, go back to the App Store Mojave download

page, it should now say Get or Download.

Do not use the mac while it is downloading or any other devices that share the same internet connection.

Don't use FireFox for this link…

https://itunes.apple.com/us/app/macos-mojave/id1398502828?mt=12

If you get a corrupted message...

Naw, not damaged, it's just that you have an old copy already in Applications, there are 2 cures...

Disconnect from the Internet & set the Date back to 2014, then you can run the Install MacsOS Mohave App in Applications, so expired Certificates are not expired.

Or... trash the Install MacsOS Mojave.app in Applications then a new copy can be downloaded.

I did that. That's why I downloaded the 2nd time. After I deleted the first one. I already read this solution. But the solution didn't work. But I didn't try setting the date back. Guess I'll try that.

Also do not use FireFox for the download. Use Safari instead. Los of recent reports that FireFox is having issues with Mac OS downloads.

I downloaded Mojave from the Mac App Store yesterday onto Catalina 10.15.6, and it delivered the installer without an issue.