IOS link handling might not be that great on older versions. Probably if you decode that QR code they might be using some custom link scheme that they register

IOS link handling might not be that great on older versions. Probably if you decode that QR code they might be using some custom link scheme that they register for their app. That's still a valid approach but should not be needed with modern phones as you can just register your website urls to be handled by the app.