The SIM is inserted, but it is not recognized.

After power on, please allow 3 minutes for the device to boot up.

Either SIM A or SIM B LED will light up depending on which sim slot the sim card was inserted.  For best practice, always use SIM A.

If none of the SIM A and SIM B LED is on, this means sim card is not detected.

Disconnect power, remove the sim card, make sure the sim contacts are clean, then insert it to the SIM slot following the correct orientation.

Refer to Quick Start Guide for detailed instructions of how to insert a SIM card.