I can buy a ticket at Air China official website, but I can't open the payment page by clicking Buy in the previous step.

I'm very sorry for the inconvenience caused to you, but during this period, this will happen due to the excessive traffic of the payment system in official website. There are two ways to solve this problem. One way is to call Air China 95583 after you place an order in official website, and then provide the passenger's name, flight number and flight date, and then issue the ticket at the call center. But if you order aviation accident insurance, it will be cancelled automatically, and you can't enjoy any activities in official website. The second method is to call Air China 95583 directly and issue tickets directly under the guidance of the agent, but sometimes the official website preferential price of some routes cannot be enjoyed. Personally, I suggest using the first method. Thank you for your support to China International Airlines. Have a nice trip!