Successfully installed 8.1 then upgraded to Windows 10 Pro. First key didn't work, but was promptly given another working key. Upgrade to Windows 10 kept failing. Just had to run Windows 10 setup with 'install updates' turned OFF

I received after the payment the key for W8.1 Pro instant within seconds after payment,
And it works ;)

Worked like it should! Excellent!

It works perfectly fine, thanks

Si funciona muchas gracias