I phone sim locked

You can trade-in a SIM locked phone. The iPhone 11 Pro Max shows a trade-in value of up to $270 depending on the condition of the phone. It does need to be paid off if money is still owed to the carrier that locked it and this is also different than a carrier that has blacklisted the phone. As ikrupp stated, the best option for you most liklely is to return the device.

Apple Trade In - Apple

Trade in Carrier Locked Phone - Apple Community

Can ı trade in locked phone? - Apple Community

Trade in an iPhone that’s Sim locked - Apple Community

The answer is absolutely no, no trade-in possible. SIM lock means it is locked to the cellular carrier it set up with. Only the cellular carrier can unlock it and you cannot use it. My advice would be to take it back where you bought it and try to get your money back.