upgrading my MacBook Pro (17-inch, Mid 2009) from El Capitan to High Sierra fails

• https://www.cnet.com/forums/discussions/upgrading-from-el-capitan-to-high-sierra-wont-download/

Attempting “FREE UPGRADE” on OS X El Capitain leads to:

We could not complete your purchase.
This version of macOS 10.13.6 cannot be installed on this computer.

Attempting to Download macOS Sierra leads to:

We could not complete your purchase.
This version of macOS 10.12.6 cannot be installed on this computer.