"We're aware of players being unable to claim their Steam keys due to the Path of Exile website being down. Our website team currently has this as their top priority and have a plan of action to restore this service to allow you to play the game! A huge thanks for the grace being displayed by those affected."
From twitter.
https://x.com/pathofexile/status/1865161690175934581I kind of expected this when I bought, but I think they'll be working on it, but I'd do something else for an hour or two. It's doubtful it'll be fixed in 15 minutes. They might've even done it intentionally to help with server load or unintentionally.