Appletv with tmobile not working

Did you follow the steps provided by T-Mobile to activate the promotion?

https://www.t-mobile.com/support/plans-features/apple-tv

You don't even need to sign out, but if you did, you will just sign in as normal after the promotion has been activated through T-Mobile.

Canceled paid subscription …

T-Mobile says that this step shouldn’t (have to) be done. Redeeming their offer stops the payments automatically for the duration of the offer.

Apple does not offer option to sign in with tmobile

Sign in with your Apple ID as usual, as that is what T-Mobile will link the redeemed offer to.

T-Mobile has a redeem procedure that has to be followed quite meticulously. You can’t skip steps and expect it to work.