1. Check if your SIM card is inserted correctly.
2. Check the type of SIM card needed for your phone model by referring to the device manual.
3. Contact your phone service provider or carrier in case the SIM seems to be working correctly.
4. Make sure that your phone is not configured to only accept a certain type of SIM, and that this type of SIM matches the card you are currently using.5. Check if your phone has any restrictions set which may be preventing the SIM from being recognized.