You will not see the Swiss Travel Pass Flex in the app until you have activated one of its travel days. Only then will you see the ticket.
To activate a travel date, please go to: activateyourpass.com. You can do this in advance already; the ticket for an activated travel day can be deactivated as often as required. Deactivation must be made before the start of the validity period at 23:59:59 (Swiss local time).