: If you have previously "purchased" (downloaded) El Capitan, it may appear in the Purchased tab of the Mac App Store.
On a Mac (running El Capitan or newer), follow the official Apple link above. If the App Store shows “This version requires OS X 10.11 or later” and your Mac is newer, hold the while clicking the link—some users report bypass. Alternatively, sign into a different Apple ID that previously “purchased” El Capitan (it was free). Mac Os X 10.11 El Capitan Iso Download