3dSecure cannot be activated

Maybe someone here can help me, I'm a bit desperate at the moment. I would like to pay for something online using my Mastercard. For some reason it now requires confirmation via 3d-Secure for this purchase. As requested, I downloaded the Sparkasse's S-ID app. In order to get the card in there, I first have to activate the card online. I did that and received confirmation of the activation. In the meantime I have even used “Card C” again