you’ll need to contact TMO to figure out that one. are you a TMO customer? was the device used on TMO  by you? how long? did you purchase this form someone and found it was locked to TMO?

the criteria that must be met as long as you purchased it from TMO and it was used on their network for the required amount of time listed in the link provided

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

How much I have to pay for my phone

You can sign into your Mytmobile account and find out there.