If your smartphone is not functioning correctly during a journey or is not able to communicate with the servers (e.g. flight mode, location services disabled, empty batterie, low batterie mode, etc), you are not complying to the requirements for the usage of FAIRTIQ.
If this happens, you will therefore be travelling without a valid ticket and you risk a fine.
If the interruption is only temporary (crossing a tunnel for example), the system keeps running in our backend and is still valid.
Please note that you are responsible to have a working device all along your travel.