When upgrading a Windows 10 Home installation with a valid Windows 10 Pro key, you’ll often times encounter some issues while trying to upgrade.
First off, you should be using the generic key for upgrading Windows 10 Home to Pro, instead of your new Pro key out of the bat:
The issue that often times occurs is that Windows will apparently accept this key and right after prompts you for confirmation for starting the upgrade process, which might then result in the 0x803FA067 error.
The solution here is pretty simple. After you enter the generic key above, you should disable Internet Connectivity *before* confirming the upgrade process startup. An easy way to do this is to activate Airplane mode under quick settings.
Windows should then be taking a moment to upgrade and reboot. After that you can activate Windows with your new Windows 10 Pro key.