I just had the same thing happen as Kahleesi44 - I click on the confirm link sent to my email & get a small window saying "Internal Error". The page then goes to the Dominion Online load symbol & spins the loading wheel icon but does nothing more.
As a follow-up, I closed out Dominion, re-opened it, & the sets I'd purchased access to are useable through the game.
As a follow-up, I closed out Dominion, re-opened it, & the sets I'd purchased access to are useable through the game.