If you are unable to access the app over a mobile network, try the following steps.
- Turn data off completely (switch to flight mode for example) for a few minutes and switch back on.
Is mobile data now active?
If not, continue with the following hard reset steps :-
- Switch off the device and eject the sim card
- Turn the iPad on (allow it to boot fully)
- Switch iPad off again - insert Sim Card
- Switch iPad on and test again.
If there's still no connection contact the carrier.
To access the app when no data connection is available, locate a wireless connection, sign in once and work off line for the rest of the day.