Did you create an account on the SBB site before buying the pass? If you didn’t, then there is no way to add your purchase afterwards, and it will not be visible in the SBB app.
But that is not a big issues, as you do not need to have the Swiss Travel Pass in the SBB app. All you need to be able to do is show the QR code when requested, and wether you do that on paper, or just buy showing a picture on your phone is not important.
The reference to the 10 digit number is for the “Swiss Pass”, which is a product that has nothing to do whatsoever with the “Swiss Travel Pass”. And you do not have the Swiss Pass, so you can ignore that.