Why do I get the «An error occured when we tried to process your request» failure on the iPay88 payment page?

Oops! We’re sorry
Error reference number : 20170413_11708424

An error occured when we tried to process your request. We’re already working on the problem and expect to resolve it shortly
If you were trying to make a purchase, please check your bank account and email to confirm that the order was placed
We apologize for the inconvenience