Try using a computer with either Chrome or Firefox, if you aren't already. Please clear your cache, make sure all fields are completed, and that your billing post code is correct.
If you have tried checking out more than two times, your credit card company may have blocked you from checking out on the site and you may need to call them to verify the charge. If you get an error message due to an incorrect billing post code any charges on your card will automatically drop off after a few days as the order has not processed correctly on our end.
If you've tried all of the above to no avail, please reach out to us via the Contact Us page. We'll be happy to try placing a manual order for you!