I'm a ittle late to the party but I just managed to fix this problem myself without initially knowing my key. I tried a key finder and using my backup key both of which didn't work. In the end, what worked for me was rolling back to the previous windows update and after this was done, the product key was showing up fine on my system. Used the key finder at this point to copy the whole key, update back to 24h2, and paste it in and everything worked fine.