First try paying your invoice directly instead of trying to place an order on the website.
Try clearing your Internet browser or if you are using a VPN, try turning it off. Your failed order may be blocking other attempted orders.
Do not use your stored credit card and manually enter your credit card information during checkout. Keep in mind, prepaid cards may cause an issue.
If this does not help, we suggest contacting your credit card company or using a different credit card.