pin de la sim

Are you trying to use another T-Mobile SIM or is the SIM from another carrier?  If the SIM is from another carrier and the number it wants is to SIM unlock the device.  The device and account owner would need to contact T-Mobile to verify they both meet all of the SIM Unlock Policy requirements.  

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

There is a SIM PIN and there is an unlock code. One is related to the SIM card and the other is related to the phone, so it is important to be clear about which one your device is asking for. 

If your phone is asking for a SIM PIN or PUK code, then that is a security feature on the SIM card. You can learn more about that and how to fix it on Resolución de problemas de error de PUK y SIM | Asistencia de T-Mobile

If it is asking for an unlock code, that means that the phone is carrier locked and you are trying to use it on a different carrier. If it is a T-Mobile phone, you would need to meet the requirements that syaoran shared above. If it is not a T-Mobile branded phone, then you would need to meet the requirements set up by the carrier it is locked to.