The most common reason your bank will decline the payment is that the billing details you provided during check-out are not fully equal to the details registered for the card you are using. Please always double-check that the address linked to your credit card and your billing address is identical. If you need to add a flat or unit number it might be better to provide this via the separate input for the shipping address instead of via the billing details. If you would still run into trouble after all, please reach out to us (info@sdmatrix.net or +31 494 28 40 81) and we will gladly find a solution together.