Our payment gateway partner Stripe sometimes declines cards because they have problems verifying that you are the original owner of the credit card. This can be because:
You have changed the cardholder name too often.
The cardholder name differs from what you have used on another Stripe-powered store in the past.
You are using a new email or address.
The solutions:
Use the same information you have used with this credit card before.
Wait - sometimes it helps to wait a little bit, up to one day.