All of our credit card transactions are processed through Stripe.
Preventing a Decline
If you did not enter your address in the registration form, some credit card companies will decline your card because they can not verify your information. You can add your address after you have registered by going to you account page.
Here is more information from Stripe about why credit cards are declined: https://support.stripe.com/questions/why-was-a-customers-charge-declined