What to do: re-click the place order, the payment form should display - 2 payment options - credit card option (post-payment), and the visa and mastercard option (prepayment).
If you dont find the second option, click "Cancel", then re-click "Place order" or "confirm" asap. The second option will surely display this time, check it, and you can load the amount you want to pay in advance, and card details. Thereafter, your ad should start running.
Hope this helps.

Mikki