Activate the Game

[BlackSoulSpirit]

Hi there i just bought the Trackmania 2 bundle on Steam and created an Acc on the Maniaplanet Software.
I tried to change the Flag but nothing happend when i clicked on use your own Picture.
Then i googled and it says that i need to activate the game for my Acc but when i go on https://www.maniaplanet.com/ and enter the steam key that i get from Steam it says

The key was not associated to your account: This game key requires Steam.

and under Authorized applications it says

No authorized applications yet.

so do i own the game or not and how i get access to the full features like changing the Flag