If your LU800 is delivered with SIM cards installed, don't remove them or install SIMs from a different unit.
Each SIM pair is designated A or B. Tapping allows you to switch between SIM A and SIM B per modem. When the unit is turned on for the first time, it looks for the SIM cards in slots A.
Loosen the two screws on the LU800 and gently pull the flap down to expose the SIM slots.
The slots are numbered from 1 to 8, left to right. The bottom row contains slots for SIM cards A. The top row contains slots for SIM cards B.
Insert the SIM cards into the slots in any order.
The following figure shows the open flaps, indicating how to hold the SIM card when inserting it into an A or B slot.
The eight external antenna connectors shown in this figure are provided on request.
Close the flaps and tighten the screws.