Hello there, artistjohn! Thanks for reaching out with this, and welcome to the forums! I think it's really great you're looking to support the YouTuber who's showing off Anno 1800 in their let's play! With that said, however - it's possible the website you're looking to purchase the game from is selling keys which are unable to be used in your region. I'd suggest asking the retailer themselves what the regional availability of their keys are, as we'd be unable to determine this from any other store except ours.
(Side note, I edited your post to remove personal information as this is a public forum! I appreciate the sincerity.)