During the checkout process, the client is requested to sellect the Payment method. And later on, after the summary page, the customer is re-directed to the Complete Order page, in which the previously selected payment method is lost.
If you select again the payment method, the purchase is correctly processed.
Attached you can find snapshot of the 2 pages in which the customer must select payment method.
We are using Sellacious v2.0.0-beta2