Using mobile app: 2 questions

The app can't make reservations. It can only forward to some of the websites where you can make reservations.

How you book reservations depends on the website. Here's an overview:

https://www.seat61.com/interrail-and-eurail-reservations.htm

And also in this thread:

• How to get Reservations :)

On the DB website, you just select "Seat only”. The DB website works for trains in Germany and some trains from/to Germany. In general only for trains with optional reservations.

For day train reservations in Italy or trains from Switzerland to Italy, you can use tickets.oebb.at. On this website, do NOT use "Seat reservation only” but add the Interrail/Eurail discount for each passenger and then select "One-way tickets and day tickets”.

Reservations for journeys within Switzerland are unnecessary (and a waste of money), except for a few panoramic express trains with mandatory reservations.

The mobile pass needs internet:

1. To activate the pass. You only need to do this once.
2. To activate a travel day (usually by adding the first train of the day to your pass).
3. To generate the QR code (tap on "Show ticket”), after adding the first train of the day.
4. At least every 72 hours.

The mobile pass can work offline after you've done action 2 and 3 at the beginning of a travel day. If it takes too long to show the QR code, then turn on flight mode.

If you still prefer a paper pass (and if your mobile pass is refundable), you could request a refund and buy a paper pass at the DB ticket office at Frankfurt Airport. That's one of the few locations where DB sell paper Eurail passes. That will however come at a cost. Or you could do an exchange through Eurail but then you'll have to wait for the paper pass to be delivered at home.

Thank you for the advice. SO just to make sure I have it right: 

1. I can use “trip planner” to ‘store’ my segments even though I haven’t yet activated the pass. 
2. I buy seat reservations on national websites (I’m comfortable with German Rail) and print them out or take screen shots on my phone. 
3. When I arrive at Frankfurt International, I activate the pass (even if leaving a couple hours later?) 
4. I link my first trip (Frankfurt to Bern) somehow to the pass and get a QR code immediately (PLEASE tell me if that’s not right)! 
5. Walk to the train. IF there’s no wifi on the train (I won’t have a SIM card yet) I can still show the QR code (as a screen shot?)

THANKS for any more help :) 

PS it seems like it would be much easier to have a paper pass! 

Every now and then, the app has a bad day and won’t show your QR code due the conductor. If this happens, just put the phone into airplane mode and relaunch. It should show it then

Also note that segments are called "journeys” in the app. The "trip” in the app will eventually contain all journeys you will do during the validity of the pass. A pass can be connected to one trip only.