sim locked

Are you a T-Mobile USA customer?  Does your account and device meet all of the SIM Unlock Policy requirements?

https://www.t-mobile.com/responsibility/consumer-info/policies/sim-unlock-policy

Hey there @fazzy, Unlocked devices are great for using your phone with any carrier in the world. Where did you purchase this phone? How long have you had it and did you ever use it on the T-Mobile network? Getting a little more information helps us provide better answers.