This depends on the rates and terms and conditions of your booking. 

If you book the FIX rate, your credit card will be charged during the booking process.

If you book the FLEX rate, payment is due on arrival, unless other cancellation conditions apply due to a trade fair or event. In this case, your credit card will be charged automatically at the time of the date when a free cancellation is no longer possible (e.g., 14 days before arrival). You will find the terms and conditions on your booking confirmation.