Installing El Capitan on external hhd

I use a Mac Pro running High Sierra from an ssd. I  am trying to download El Capitan from App Store and install it on an external hhd, but App Store refuses on the ground that I run from an ssd. Message says "We could not complete your purchase. OS X can't be installed on 'ssd' because the version of macOS is too new."


App Store "Download" button does not offer a choice of "explaining" my intention. Any suggestions?




iMac Pro, macOS High Sierra (10.13.3)

howapple - hello


OK, me again!


It looks like App Store "remembered" my original El Capitan download for another machine, eons ago. I should have used the "Purchased" button in App Store. Looks like problem has been solved. Anyway, thanks to those you took the time to read my original post.