Sim Not Supported

See this guide and follow ALL the steps provided:--> How to unlock your iPhone for use with a different carrier - Apple Support

Apple can't unlock your iPhone for use with a different carrier. Only your carrier can unlock your iPhone.

Giulio

Apple doesn't unlock your device. Your carrier does. Ask them.

It's not an Apple problem. It depends on your previous carrier.

Regards

Giulio

That's a con. Apple has nothing to do with unlocking you from that old carrier to start using a new one.