I am not able to activate Adapty in flutter

I am configuring Adapty according to this tutorial: https://docs.adapty.io/docs/flutter-configuring. Anyway, I don't think the documentation is up to date.

When i am trying to execute this line of code:
await Adapty().activate();

Android Studio tells me this This expression has a type of 'void' so its value can't be used, so, i can not even run the code using this... When i remove the void, I am able to get to a page with iOS styling, but I see the alert saying Adapty Error 20, adapty was not initialized

Thank you for your answer.