On three occasions I have recently booked tickets on my PC and after waiting, have received the following message on what should be the confirmation screen:
We've encountered problems during the payment of your tickets. Please try again, or contact us for further support.
On the first occasion I had already started re-inputting the details and was almost near the end when I heard an incoming email alert on my phone. This email showed my booking confirmation reference. On the next two occasions the same message was received and I waited for email confirmation, which I got.
This is a poor error message. I don't know what triggers it but I am sure that many people are unnecessarily paying twice.