This page demonstrates protected credit card form protected against a variety types of fraud.
Only prefilled card details are correct. When you change them, the system will check if you tried to perform Card Cracking. After 3 unsuccessful attempts is this visitor flagged as suspicious and cannot place orders anymore.
If you have a positive chargeback history, can you place your order? Try to place a regular order after two chargebacks.
Simulate a visitor using a stolen card. Can you place another order from the same browser?
You can also try switching to the incognito mode or clearing cookies.