Two mistakes.
Firstly, buying a key from ebay.
Secondly, trying to clean install Windows 10 using an 8.1 key.
Firstly, the eBay key has been refunded, OEM, no thanks. I've got a retail key from a reputable key site now.
Secondly, read the thread. I'm not trying to use the 8.1 key.
Anyway, back to all the other replies. Thanks for your input and how you got it worked. I am 100% sure it says it's activated and it currently does (did the upgrade again last night). I did notice something different, I assumed the 'clean install' bootable image MS create for Win 10 was universal. I think this isn't the case. I created the image before I had the retail key. I will re download from my current installation. But think I will wait until this new release.
From what I'm aware of it is universal, the iso tool from Microsoft, and it downloads the corresponding version of windows 10, based on what 8 1 licence you have.
And besides, you have 10 activated which means it picked the right windows 10 version
Glad you got it going. Enjoy.
Thanks mate, I'm cursed lol.