There can be several reasons for this, which unfortunately are not always given to us by the credit card company. Alternatively, try to complete your payment with a credit card via Paypal. You do not need a Paypal account for this and enter your data there as usual. If this does not work either, please contact your credit card company or use another payment method such as Paypal, Postfinance Card, e-finance, purchase on account, Twint or prepayment.