half fare card

You add to your profile that you have a Half Fare Card, then you get the HFC price.
Its the little face icon at the bottom on the right.

Now that I look at it, you have to add that your SwissPass account. Log in and go to personal details and at the bottom choose discount cards, including the Half Fare Card.

I don’t use the app but I do buy our tickets online on the website. That has the Half-fare price as the default setting. I don’t need to do anything like enter a code from the card to get the half-price fare.

The half fare card doesn’t work like you think it does. There is no verification that you have the HFC when you purchase a ticket, it’s on the honor system. Then when tickets are checked ON the train by a human they will ask to see your HFC (QR code from email or print out, whatever you have). You can certainly purchase half fare tickets on the app, even when you don’t have any “proof” loaded onto the app. Same as at the ticket machines. They don’t require proof. You just say you have it and then provide it during ticket checks.

But on the app, it will not offer you the half fare price when you go to buy the ticket on the app if you have not loaded that you have a Half Fare Card on your profile. There is no confirmation that you do have the HFC. So the problem is when you try to buy tickets using the app. Sure, you can buy tickets from a kiosk or a manned ticket window at half fare without showing the HFC, but the OP's problem is they want to buy tickets with the app. example: I am on my app right now, and for Luzern to Zurich airport, it only offers the full fare price of 31 CHF.

I now see that you can add an HFC on the app. It is on the bottom of the screen in the middle with an icon that looks like a tiny QR code. Click on that and the next screen is "Tickets & Travelcards" Below you will see "Manually entered travelcards". Click on the button below "Enter travelcard". The next page select "Half Fare Travelcard", then hit "Save". Now on my app it will give me a price of 15.50 CHF, the HFC price.

You can buy tickets on SBB at half fare. SBB doesn't check that you actually have the half fare card, it's up to the train conductor to check.

@ wcbhkids, Yes, but we are talking about buying tickets on the app. If you have not added that you have an HFC on your app profile, the app will not give you the HFC price. We are not talking about purchases made on-line or from a kiosk or ticket window.

@Sam
You are wrong. Although one could create a SBB profile and "load" the half fare card, it's not necessary, and in fact, you don't even need a profile at all to use the app. The first time you try to purchase a ticket as a guest, the SBB app will present you with various options, all you need to do is select the half fare option. The app does not in any way attempt to verify whether you actually have the half fare card. The app will remember your choice and always present the half fare price for future purchases. As I said before, the conductor may ask to see your half fare card.

If you are still having trouble with the app, an SBB representative can help you with the app setting. Keep proof of the half fare card handy as it is needed when confirming your ticket to the train conductor (or boat).

Make sure to add payment information to get the most out of the SBB app.

But I already have the app, with my credit card, so I have no option to "register as a guest". The app knows who I am. And I believe that is the OP's issue.