First of all, it is necessary to determine at what stage the payment problem arises. If your payment button is not active, most likely you have exceeded the limit of the verification level. You can get additional information in the support chat by specifying your order ID.
If the problem arises after entering information about your bank card, please note that your card's support for 3D Secure online payment technology is a required condition. If your card supports this technology, but there is still no possibility to make a payment, you may be trying to pay less than the minimum deposit (25 eur), or the transaction is rejected at the stage of checking your bank payment (exceeding the allowed limits for transactions on the Internet).