This problem may be caused by the following situations. Please perform troubleshooting based on your actual conditions:

There are two cases where the PIN code appears after power off and reboot:

1) One is the password lock of the SIM card, which requires a 4-digit password lock. The SIM card will be locked when if you input the wrong password 3 consecutive times, and then you need to call the operator or use the PUK code on the card box to unlock the card.

2) The second is that it is the unlock password, which should consist of 6 digits. If you forget the password, you may long press the volume up button and the power button simultaneously to enter the recovery mode to perform a factory data reset, or contact the customer service of the corresponding platform to perform a version upgrade to solve the problem.