NOTE
We are sorry that the payment process with Credit Card is making problems for the one or the other (Credit Card declined). We are told by NextEvent that there is no possibility from their side to solve this problem; this depends on either the personal credit cards or the Datatrans firm which proceeds the money via credit card. You can contact your bank and have the restrictions regarding your payment for NextEvent lifted. As this will take some time, we recommend that you follow the procedure described below: 
Please try the following:
Book your tickets in the ticket shop and choose payment with invoice prepayment.
You will get an invoice and with this you have the choice to pay with bank transfer or with credit card (qr code for payment with credit card on page 2 of the invoice).
With this you can secure the Early Bird price and have the choice to do it without stress in the next 10 days.
Tickets will become available for delivery (email with download links) as soon as payment of the full amount has been registered (this takes about 5 days).