PostListActivity.kt

class PostListActivity : AppCompatActivity() {

    @Inject
    lateinit var viewModelFactory: ViewModelProvider.Factory

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_post_list)
        getAppInjector().inject(this)
        val vm = ViewModelProviders.of(this, viewModelFactory)[PostListViewModel::class.java]
        vm.posts.observe(this, Observer(::updatePosts))
    }
    
    //...
}

PostListViewModel have 2 inputs in constructor ! idont see in activity or your di or any files in your medium example