- You recently moved, and changed your address at the bank, and
- You are attempting to checkout with a saved card on file.
This is a known issue that currently exists due to the way we save your card in our secure servers (using Stripe). Basically when you saved that card the first time, it saved it with the billing address you used then. This means if you moved, when we try to charge your card on file, it is attempting to also validate that old and out-of-date billing address.
SOLUTION: Edit the card, or delete it and re-enter your details.
Currently, you cannot edit your card during checkout if you're reusing a "Saved Card on File." That's because the saved card and address are associated with each other on our payment gateway's servers, and you'll need to update the card and address at the same time.
If the NEW card also fails, then it's most likely a problem with your card or the address on file at your bank. Please give them a call and make sure your information is current and correct - if this can sometimes be an issue if you've recently moved to a new address.