You need internet:

1. to activate the pass (just once)
2. to activate a travel day (also on a continuous pass)
3. to generate the QR code (the actual ticket), by tapping on "Show ticket”
4. every 72 hours

You can do 2+3 while you still have wifi. I wouldn't do that in advance, but on the day itself. You can only cancel activation of your pass or a travel day until 23:59 CET before validity starts. If something happens after that, e.g. you wake up ill, then it will be too late to cancel and you'll lose a travel day.

After you've done 2+3, you can add and remove journeys as you like. The QR code remains the same for a travel day.

Thank you, rvdborgt! That is very helpful!
David

Note that there are many mobile service providers in Europe which will provide loads of data and phone connectivity for €15 or less a month.  Thanks to the EU you can use this service across most of Europe (I think Switzerland may be an exception) without paying any roaming fees.

In other words, you could buy a SIM in a shop in the first country you land in and have internet access for a month for the price of a couple of coffees.

They keep changing the product names, but effectively most of the providers will sell you a SIM (or give it to you for free) and then all you need to do is buy credit online, or in a convenience store.

In the UK - https://www.tescomobile.com/no-contract-sim.  In most of Europe - https://www.lycamobile.ie/en/bundle/go-unlimited/

Just make sure that you don’t sign up for a contract or commit to a recurring payment and your connectivity problems are over.

Exceptions include all non EU member states, i.e. Switzerland, Liechtenstein, San Marino, Vatican City, Monaco, Andorra, Norway, Iceland, Serbia, Bosnia, Montenegro, Kosovo, Albania, Turkey, Moldova, and the Northern Part of Cyprus.

San Marino Vatican and Monaco are too small to bother about it, Andorra Liechtenstein and Switzerland are often excluded, whereas Norway and Iceland often Included.

Serbia Montenegro Albania Kosovo Turkey and Moldova are almost never included.

You need to check the fine prints

Norway, Iceland and Liechtenstein are always included. Last time I went to the UK, it was also (still?) included. 

From https://europa.eu/youreurope/citizens/consumers/internet-telecoms/mobile-roaming-costs/index_en.htm

You need internet. 

Yes, but not continuously, see my first reply.

@Mukhammad @Camilo. Wouldn't it be a good idea to put these internet requirements in a KB article or in the mobile FAQ? The FAQ touches on internet requirements in a few places but there's no overview like the one I posted here. It would also be much easier to be able to refer to it instead of typing it up every time :)

@rvdborgt Thanks for letting us know! The information about the internet requirement is put according to some steps mentioned on the "User guide for mobile Passes" in the App. This guide can be seen in the App by going to "More" → "Help centre" → scroll down to "User guides".

Also to generate QR code by "Show ticket", I checked just now that it doesn't require us to be online. Please let me know if there's something else I can check and report to the App team. Thank you! :)

Hm, yes, but the information about when you need internet is again quite scattered there.

It was when I last tested this… I'll retest. It would indeed be good if it isn't needed anymore.

As long as the journey is saved to the Trip and added (activated) to the Pass, I found showing the ticket can be done offline. Of course let me know if you find it different on your end 

I think you both may be misunderstanding each other.

It is activating the Aztec (QR) code for a travel day by activating the first journey of the day that requires internet connection, once the day has been activated internet is not needed for showing the ticket code or for adding/removing journeys.

Internet is needed for cancelling a travel day.

Indeed! If we cancel a travel day wtihout any internet connection, a pop-up will appear notifying to check the internet connection and try again

I just did 2 tests

Test 1:

1. Save a journey for a future date to My Trip.
2. Add it to My Pass.
3. Go to My Pass.
4. Tap on the active pass. (The app shows “loading your tickets" or something similar)
5. Turn on flight mode.
6. Tap on "Show ticket”.

Result: QR code shows.

Test 2:

1. Save a journey for a future date to My Trip.
2. Add it to My Pass. (Waited until the switch turned yellow and "Travel day” was added to the date.)
3. Turn on flight mode.
4. Go to My Pass.
5. Tap on the active pass.

Result: The pass won't show. The app becomes unstable, crashes and/or restarts, each time I tap on my active pass. In My Trip, the new journey is shown as added to the pass. I suppose loading the tickets now doesn't work.

Shall I create support ticket? I had error logs turned on. IMO, it should load the tickets immediately after activating the travel day and not wait until you go to your pass. In addition, lack of connectivity should never crash the app.

@rvdborgt that must be a bug. Did you also have the latest version of the App?

I did the same test 2 you mentioned, it didn't crash on my end. In this case, I'd suggest you to create a support ticket to the CS

Yes, there is definitely something wrong with your app there, I had tested this before my last post and it all worked offline except for the day activation/deactivation and certainly no crashing.

Which version are you running? Mine isn’t up to date, currently on 40.2.0 on Android.

This is 40.8.0 beta… maybe I should go back to the release version.

Update: this bug seems to have been fixed in the meantime. After adding a journey to your pass, you don't need to tap on Show ticket anymore to be able to show the QR code later without internet.