All the FoxBox belonging to GT family with the SIM card flexible extender.
The machine is unable to use the Modem2 SIM card to send messages, due to a bad electrical connection between the flexible extender and the on-board modem slot.
1) Remove the SIM card from the SIM card flexible extender;
2) Remove the Modem from its slot, gently pushing the metal clips;
3) Reinsert the Modem in its slot, while mantaining the flexible extender in the correct position;
4) Reinsert the SIM card and restart the machine.
Attention: you have to be really careful while removing the modem in order to avoid damages to the flexible extender!
The following video will clearly show you how to reinsert correctly the Modem and fix the bug.