I tried to pay w/ a master card, but this is the error I'm getting:
Your payment was successfully authorised by the bank but the Protx Servers were unable to inform Live For Speed of this fact. Your payment will be automatically cancelled and your card will not be charged. This may be a temporary connectivity issue so please try your purchase again later by returning to the Live For Speed web site. If this problem persists please contact Live For Speed and e-mail [email protected] to make us aware of the issue.

Edit: Retried, and it worked.

How's about doing what the error SAYS, and contact the devs! There's absolutely nothing we can do for you.

I had a similar problem when i tried to pay for S2. I had to wait about an hour before i could pay.