In order to buy tickets and view them in your app, you must have created an account before purchase and being logged-in while purchase. Later you have to log-in in the SBB Mobile App using the same credentials. By doing so, the tickets are viewable through the app. Some tickets, mostly international tickets, cannot be viewed in the app, however.
I assume you bought the tickets as guest or do you have an account?
In order to benefit from Half Fare tariff, go to the app, do a dummy booking, just *before* hitting the Buy button, modify your personal details hitting the pen icon. Tick the ½ checkbox next to your name. This way, the app will always show ticket offers at reduced fare. You can do the same for other co-travelers should you wish buying tickets for them using your SBB Mobile app. For this, see Profile tab, then Co-Travelers.
Kindly note, the reduction granted is not always 50% off, it might be less, this depending on the route or ticket type. This is why Half Fare defines itself as “up to 50% off”.