Can't download Sierra because incompatible

[Garyloffler]

Went to the App Store but it will not let me download the latest version of Mac OS because it is not compatible with the software running on my Mac. Tried using the Purchased button to re-download a previous download but it gets the same incompatible error. Is there another way to download slightly older versions?

 

[Stork]

You'll need to have a System Definition like iMac14,2 because the previous El Capitan (and earlier) default Mac Pro 3,1 System Definition won't work with Sierra.

 

[Garyloffler]

You'll need to have a System Definition like iMac14,2 because the previous El Capitan (and earlier) default Mac Pro 3,1 System Definition won't work with Sierra.

I am currently running Yosemite 10.10.5 on a previous TonyMac build. I want to start over with the latest version, but the app store won't let me download it. Is there a workaround for downloading the file without a true Mac?

 

[P1LGRIM]

I am currently running Yosemite 10.10.5 on a previous TonyMac build. I want to start over with the latest version, but the app store won't let me download it. Is there a workaround for downloading the file without a true Mac?

As @Stork said, you just need to change your system definition to that of a Mac which qualifies for the upgrade.
iMac14,2 is suggested.

You can download any version that you have previously downloaded from the Purchased tab in the App Store app.