What am I doing wrong in Android development in Kotlin language?

Question

android studio

There is a task from the application to request data from the server (login) and print it.
1. In build.gradle I include retrofit

implementation 'com.squareup.retrofit2:retrofit:2.5.0'

2. In the manifest, after the tag, I write that I need permissions to work with the Internet

<uses-permission android:name="android.permission.INTERNET" />

3. In MainActivity I write

interface APIService {
    @get:GET("http://api.sample.com/users/user/list")
    val users: Call<Users?>?
}

Androyd studio stupidly swears at everything and nothing works