Hi there and welcome
Did you just receive this phone? And who was the original carrier?
ok, the error message means the phone has been locked, usually this occurs when you try to use the phone with another carrier.
If this is not the case, then there will be an issue with either your account or the Sim card.
Call(###) ###-####have them check your account and remove any restrictions on it then restart the phone and see if this removes it.
If not you will need to have them send out a new sim card which they do at no charge.
Let me know please how you go.