Sim not supported

If you are getting the "Sim not supported" message, it normally means the iPhone is locked to a carrier / mobile service provider that is different to the one the Sim card is for.

Where did you get this new iPhone exactly?

Did the seller tell you it was locked to a carrier?

You will need to contact the seller and ask her what carrier it is locked to.

You then need to contact that carrier and request the unlock the iPhone. They may deny the unlock if you are not a customer of theirs however.

click here ➜ How to unlock your iPhone for use with a different carrier - Apple Support

Try and install a carrier settings update

1. Make sure that your device is connected to Wi-Fi or a cellular network.
2. Tap Settings > General > About.
3. Follow the onscreen instructions to install your carrier update.

If this is not working you want to contact your carrier for further support