High Sierra installer download fails on Mac App Store application

Currently running High Sierra (HS) on this 2012 iMac computer but want to do fresh install to a different drive.

I click on the link presented in How to download and install macOS - Apple Support for the HS installer. It opens a page in the Mac App Store App that's clearly for HS. That part works.

I click on the "download" button and for a few seconds it says "calculating" and something about a "minute". About 10 seconds after clicking "download" I get a message saying "macOS High Sierra failed to download" and "Use the Purchased page to try again." I go to the purchased page and there is no mention of High Sierra. The only OS installer is for an El Capitan installer I downloaded a few years ago.

I am using an old Mac App Store application but I have used it for other applications and it "gets" them. This must have worked at some time in the past because I must have used it to upgrade from my old Mavericks to High Sierra a year or two ago.

I have looked in my Applications and Downloads folders and there is no installer file there.

I have been trying this for several days now so I don't think it's a temporary server glitch.