I have had this exact issue myself having a secondary account within my SE account, it works with the first account, but the bank actually blocks the second accounts charge, which is why it works on SE store or Crysta, but not registering the same card as a payment method or attempting to pay directly for the sub.

I would buy the Crysta via PayPal and then try next month to add the card, since you have the 601 it will take an unknown amount of time before you can reuse it on the mogstation as a payment method.