Hi RonG,
According to Windows, the users can only upgrade from Windows 10 Home to Windows 10 Pro and activate their device using a valid product key or a digital license for Windows 10 Pro. The users can also buy it from the Microsoft Store. After getting the Microsoft 10 pro upgrade key, the users will need to select the Start button and open up Settings. Then they need to open the Update & Security window and search for Activation there. They can type out their key here and the process will start immediately.
Meanwhile, as far as I know ,we could use volume license key to activate Win10 Pro but not upgrade. A volume license is a convenient way for large businesses to purchase Windows licenses in bulk. You may not legally upgrade from Windows 10 Home to Windows 10 Pro using the volume licenses. Windows desktop VL's are upgrade licenses - you already have to have a qualifying OS in order do use the license, i.e., a Pro version of Windows. You can't use it on a machine with no OS or with one that came with a Home OS.
More detailed information about VL information about upgrade from Win10 home to Pro, I suggest that you could contact volume license center
https://learn.microsoft.com/en-us/answers/questions/222924/upgrade-windows-home-to-windows-pro-with-a-volume.html
https://www.microsoft.com/Licensing/servicecenter/default.aspx
Best Regards,
Carl