Sometimes the hardware is perfectly fine, but the phone’s software has crashed or hung up. The phone’s modem (the component that talks to the cell tower) might need a "reboot" to recognize the card again.
This is the quickest fix and works if the issue is a minor software glitch. invalid sim means
From a system perspective, “Invalid SIM” indicates that the device has detected a SIM card but fails to establish a valid authentication or registration process. It differs from “No SIM” (absent card) and “SIM Locked” (requires PIN). Typical scenarios: Sometimes the hardware is perfectly fine, but the