This question already has an answer here:
I have a Mac Pro 1.1 with OS X 10.10 Yosemite and Piker Alpha bootloader. I’m trying to download OS X 10.11 El Capitan from the Mac App Store and get the following error message:
Your Purchase Could Not Be Completed.
This version of OS X 10.11 can't be installed on this computer.
Is there a workaround for this problem? I have no other compatible Mac at home.
I only want to download the dmg file to edit it manually.