If you see an error message saying "SIM card not detected" or "Unknown SIM card," it's important to take action to identify and resolve the issue.
First, check the SIM card itself. It may be damaged, dirty, or improperly inserted into the device slot. If you attempt to clean the card or the slot, be cautious not to damage the contact surfaces of the card.
Additionally, ensure that the card is inserted correctly, as improper installation can lead to errors.
Another possible cause could be the incompatibility of an old SIM card with a new phone. Modern devices often require updated SIM cards to support new technologies. If you have an old phone with an outdated SIM card, it might not work in the new device. In such cases, it's advisable to contact your mobile operator for clarification and possible card replacement.
Moreover, issues may arise due to software glitches in the phone or incorrect network settings. For instance, a cache error or incorrect settings can lead to connectivity problems.
It’s worth testing the SIM card in another phone. If the second phone also fails to recognize the card, the issue is likely with the SIM card itself. In this case, you should reach out to your provider to check if the card is active and if there are any account issues. Sometimes, a SIM card may be blocked for various reasons, such as outstanding debts.
If the card works in another device, the problem might lie in your phone's SIM card slot. In this situation, you will need to visit a service center for diagnostics and repairs.