The order status shows "payment failed", what's the reason?

There are 3 possibilities that cause payment failed:

1) PayPal or Worldpay problem. Usually the PayPal system will prompt up the reason when the payment failed. In this case, you can contact PayPal for help.

2) Credit card problem, such as credit card expired, overdraft, etc.

3) Network problem, the network delay influence the payment process.