Our Chinese customer sometimes struggle with error 9999 and this problem is currently being investigated by our Payment providers.
In the mean time you can proceed through the basket using the old Paypal FrontEnd.
1. During the initial Paypal screen choose the option to pay with Debit card:
Credit or Debit Card
2. Change the country to China.
3. ....and the old PayPal interface will be displayed
4. You will be able to order without the 9999 error.