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

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

Also if you're a Tmobile customer and after 40 days your Pixel 6 will automatically unlock even if it's on EIP.

Hey there @olarewajujoel Unlocking a device is great because then you have the freedom to use it with whatever carrier you need. There are a few requirements that need to be met for the unlock to be possible. Was the device purchased from T-Mobile on your account? How long ago did you get this phone? Have you already downloaded the T-Mobile Device Unlock (Google Pixel Only) app from the Play Store?

A little more information will give us the ability to provide more helpful guidance.