Two things I noticed: the Find Trains button paused the screen a while but did nothing else so I'm not sure if it worked or not and the London Overground station Bush Hill Park that my ticket went to was not listed so I had to enter the nearest (Enfield Town). I also tried using the intermediate station London Waterloo but got exactly the same message whenI submitted.
Hello Andy, we haven't had any reports of the website not working at present. Would you be able to tell me the exact journey that you were trying to claim for?
Generally when issues pop up with the odd customer, it's either a network issue or (for whatever reason) their default browser will display the website incorrectly, and so changing browsers will fix the problem.
Change of browser did the trick, Google Chrome did not work for this site