How do I unlock the sim to my iPhone if I just bought it from someone
How do I unlock my iPhone if I bought it from a stranger and the sim is locked
iPhone 11, iOS 16
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If there is a SIM card that is not yours, take it out of the iPhone and insert your own. If your own SIM card asks for a PIN code and you do not have it, then you must contact the Carrier.
Another possibility could be that the phone is Carrier Locked. If you want your iPhone, Carrier Unlocked so that you can use SIM cards from other providers, you must contact the carrier where your iPhone was purchased.
You can find more useful information here:
How to unlock your iPhone for use with a different carrier - Apple Support