"sim not valid" problem

This problem can't come on startup. It usually comes after the phone asks Sim PIN and after entering the PIN, the message comes " Sim not Valid ". First make sure that the phone's Sim is unlocked. Also note that it can be a faulty Sim. Also remember, have you entered a different carriers Sim. If yes, it will ask for Sim PIN. If it is entered incorrect then it will say the Message. Also check that is the Sim faulty. Try confirming by trying the Sim on any other phone.
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