I once bought a Windows license from a third-party seller, thinking I’d save a bit of money. They swore up and down that it was genuine, but when I tried to activate it, the system rejected the key. I was pretty frustrated, but like you, I didn’t want to give up. I ended up using a kms tools activator to get around the issue, and it worked. That said, I later learned it’s always a bit risky buying from non-official sellers.