SIM code blocked

If you are trying to change, activate, or de-activate a SIM PIN, you MUST first know the PIN that’s currently set. (even if it’s not activated)

If a SIM’s PIN protection is active, the PIN must be correctly entered with every “power-on” cycle before the SIM will allow mobile network operation.

If you didn’t set the PIN yourself, carriers generally set all their SIMs to a default; contact them for assistance.

See additional information here:

Use a SIM PIN for your iPhone or iPad - Apple Support