I am buying a ticket from Walmer to Hereford on 6/6 returning on 7/6. The SouthEastern app is offering my ticket for £108 and the itinerary includes the 8.30 train from Walmer to St Pancras which is High Speed and arrives into St Pancras before 10am so I know it's a peak service. How could a Super Off Peak ticket be valid at this time? Is it because I am travelling onwards to Hereford? Has the app made a mistake? I've attached a screenshot.
Welcome to the forum. The app is correct to offer a Super Off-Peak ticket for the journeys you're looking at, and any other ticket site would offer you the same ticket as well.
Time restrictions depend on the ticket you hold; trains aren't blanket "peak" or "off-peak". In this case, a Walmer to Hereford Super Off-Peak ticket has no restrictions between Walmer and London. It only has restrictions between London and Hereford, and by leaving Walmer at 7/8am you are departing Paddington long after the morning restrictions end.
You can look up the restrictions for any particular ticket using the associated two-character restriction code - for example, the Super Off-Peak ticket you're looking at has code YQ. As you can see on
nre.co.uk/YQ (which is the link that would be printed on the ticket), the restrictions only apply at Paddington, Waterloo, Reading etc.
Online booking sites have electronic equivalents of these restrictions, and use them to determine when Off-Peak and Super Off-Peak tickets can be sold.