Yesterday someone stated that they spoke with someone at EA (how's that for hearsay) about this issue. (They play on Origin.) This got buried in another thread.
Anyway. They were told that yes, indeed, the site is not working properly atm. EA was saying it would probably be 24 hours before it was fixed, although the 24 hours have passed and it's still not working properly.
I had wanted to purchase something else as well as the booster. When I took the booster out of my cart, it worked. So basically, they don't have all the connections set up yet for us to be able to purchase the booster.
From a personal standpoint, I have no objections to the booster, and I will purchase 1 of them. But I will only purchase one for my 4 accounts, because that is all that is needed. (I play Siege and my 'crafter account' can use this booster - the other accounts can get their topiaries or whatever from my crafter. The new house tiles are 'okay' imho, but not so fantastic that I feel I must have it on all my accounts so they can redesign their houses.)