It depends what place of living you got, when you are from the us and own a us credit card, it is not a problem to book domestic flights all the way through in First or business class.
But when you are ling in europe and don't have a us credit card, you simply don't get the offer to book certain routes in business class or first.

Make shure at the time of booking there is no word from the main cabin,this means economy.
You got 24 hours to cancel this booking for free.