When I stated it was a paper pass by ticking the box, the yellow button leading to the next (input passenger details) page became inactive. I could only activate it by ticking digital pass, then onto the next page where passenger details were input, then back to the previous page to tick the paper pass box, then forward again to passenger details to now fill in start date box, then forwards to payment.
Maybe the system just crashed on me, however I got there in the end and with discount of 15% too!