i bought a new phone sim is not supported. phone is locked

w37 wrote:

I bought a new iPhone from someone on marketplace and when setting it up, it said Sim is not supported contact your carrier to unlock phone

call that someone and ask who the carrier is, or better yet, return the phone and get your money back.

You did not buy a “new” phone. You bought a gray market possibly used phone.

Only the carrier it is locked to can unlock it for use on other networks. Note that if you are not a current or former customer in good standing of the carrier it is locked to, they are unlikely to unlock it for you.

Above replies are correct.

You may well have bought the remainder of somebody’s outstanding cellular plan, too.

The All Too Common SAD Reality of Buying a used iPad/iPhone - Apple Community