Hello, I get this message when trying to download High Sierra:

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 High Sierra App in Applications, so expired Certificates are not expired.

Or... trash the Install MacsOS High Sierra.app in Applications, empty trash & restart, then a new copy of a more recent version can be downloaded…

Don't use FireFox for this link, it’ll offer strange erroneous errors…

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

Delete Install macOS High Sierra from the Applications folder and re-download while in Safe Mode.

How to use safe mode on your Mac - Apple Support

lkq111 Said:

"Hello, I get this message when trying to download High Sierra:"

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Use Ethernet:

The file may be corrupt due to WiFi. So, try using Ethernet, instead of WiFi, to download this. Ethernet gives a more reliable method of data transfer.

Good news, good work, take care my friend! :)