In rare occasions it might happen that you have set up Tickera pages in such way that they have parent pages. Not that it is anything wrong with setting up pages like this but this might cause issues on the payment confirmation and order details page.
Luckily, the solution is very simple:
All you need to do is to navigate to Tickera Settings and simply hit Save Changes button and that's it. Problem solved.
If, however, you did this but the problem still occurs, then navigate to Tickera Settings -> General tab and set Order Details Pretty Links option to No.
Of course, if none of this helped, please submit a support ticket to support.tickera.com and our support agents will check out what might have happened.