I've been trying for hours to book a ticket on Air China's Germany website - each time I press the confirm button on payment, an error pops up. I've tried AMEX, Mastercard & Visa credit cards, and used Chrome, IE, Firefox & Safari. The option to pay with PayPal doesn't work at all - the screen just loads for 2min and then an error appears.

Why is it impossible to book an Air China flight? Do you need a credit card issued in the same country as the website you are on?