To make a long story short, the quest is currently bugged and cannot be completed.
The image below shows the requirement that cannot be met.
Why can't I complete it?
What can I do?
Just be patient. Leave the quest open in your questbook. That way you can complete it as soon as it is fixed and claim the reward.
You are not missing any other quests, by not completing this one.
It seems like you can finish this quest after all.
Thanks Muerte66 for sharing your solution: