An error message pops up in 1of 3 scenarios:
When an answer box requiring mandatory information hasn't been filled out before clicking 'Submit Payment'. Be sure to fill out all the required information before confirming the payment.
When invalid credit card information has been entered. Verify that the card number, name (as written on the card), expiration date and CVV number are all correct. Ensure that your remaining credit limit is greater than the payment you're making.
When there's an error in processing the payment. If this error persists, you'll simply need to try again later.