Before connecting to the Web UI, make sure that your SIM card is properly inserted and that the PIN is disabled or entered.
Once you are in the Web UI, you can notice that several statuses can be written next to the SIM card status line:
• No SIM Card or SIM Card Invalid: The SIM card is inserted and detected but not working due to the PIN code. The SIM card is not properly inserted in the device, or no SIM card is inserted in the slot.