Problem

LtAP log messages indicate, that the SIM card is not inserted:

00:05:35 lte,async lte1: sent AT+CPIN? 
00:05:35 lte,async lte1: rcvd +CME ERROR: SIM not inserted

Solution

The modem does not see any SIM cards inserted:
+CME ERROR: SIM not inserted

Please check if you are using the correct SIM slot. For the modem inserted in the bottom mini-pcie slot (this is the slot where modem that comes pre-installed in an LtAP lte kit is located) you need to use either sim slot 2 or sim slot 3. And the used sim slot needs to be selected in RouterOS.

CLI command to select the sim slot:
/system routerboard modem set sim-slot=2