Skip upgrading W8 Pro to W10 and install W10 and use key from W8 Pro?

I am sorry to have to ask this question, but I do not have the points to just comment on some of the similar questions:

Windows 10 Clean Install and Windows 8.1 Product Key [duplicate]

Can I install the free Windows 7/8 -> 10 upgrade on a new empty drive?

Also, those might be outdated because Moab commented that with W10 build 1511, things might have changed a bit

Starting with W10 build 1511, you can use the W7 or W8 key on a clean install.

So, I have a Windows 8 Pro install DVD with a valid key and am trying to use that key on a new Windows 10 installation.

I used the Windows 10 Media Creation to create a bootable Windows 10 (I was not given an option for Windows 10 Pro) USB and I used that to install fresh Windows 10.

The windows installation let me use my Windows 8 Pro key when I was first prompted at the install, but after the install was done and I tried to activate the new Windows 10 installation I was told that the key is not working...

Can I skip upgrading Windows 8 Pro to Windows 10 and just install Windows 10 and use the key I have from my Windows 8 Pro?

EDIT: After an update now I am getting this message: This product key is already being used on another PC. Error code: 0x803FA071

TL;DR

1. Get a bootable WIN 10
2. Install WIN 10
3. Enter they key you have from your WIN 7/8
4. Go to setting and activate the newly installed WIN 10
5. If your activation fails, enter your key again.
6. That should fail again but will give you the option to call support
7. Call support and they will help you finish your WIN 10 activation

The long story.

Something happened, and my Windows 8.1 Pro stopped working and I had to reinstall it. I have a Windows 8 Pro installation DVD that I got from Amazon a few years back. I used it and installed Windows 8 Pro on my PC. Ultimately I wanted to upgrade to Windows 10 Pro, but it was taking too long to update Windows 8 to 8.1, so I installed Windows 10 Media Creation and created a bootable Windows 10 USB. Using the bootable USB, I installed Windows 10 Pro on my PC, and that is where the pain started. I did some googling and found that with Starting with W10 build 1511, you can use the W7 or W8 key on a clean install, but I could not find how to actually activate the fresh Windows 10 installation. After several tries to activate I finally called support and they helped me out.

Note: A side effect of skipping the Windows 7/8 upgrade to Windows 10 is that support had to invalidate my Windows 8 product key and give a new key.