How to call an activity method from fragment | Start Activity from Fragment

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
        xmlns:android="https://schemas.android.com/apk/res/android"
        xmlns:tools="https://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:padding="8dp"
        tools:context=".MainActivity">
    <FrameLayout
            android:id="@+id/frameLayout"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />
</RelativeLayout>

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Toast

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        var fragmentManager = getSupportFragmentManager();
        var fragmentTransaction = fragmentManager.beginTransaction();
        fragmentTransaction.replace(R.id.frameLayout,  SampleFragment()).commit();
    }
    public fun fragmentMethod() {
        Toast.makeText(this@MainActivity, "Method called From Fragment", Toast.LENGTH_LONG).show();
    }
}

class SampleFragment : Fragment() {


    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        arguments?.let {

        }
    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_sample, container, false)
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        btnClick.setOnClickListener(object:View.OnClickListener{
            override fun onClick(v: View?) {
                (activity as MainActivity).fragmentMethod()
            }

        })
    }

}

<FrameLayout xmlns:android="https://schemas.android.com/apk/res/android"
             xmlns:tools="https://schemas.android.com/tools"
             android:layout_width="match_parent"
             android:layout_height="match_parent"
             tools:context=".SampleFragment">

    <!-- TODO: Update blank fragment layout -->
    <Button
            android:id="@+id/btnClick"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:layout_gravity="center"
           android:background="@color/colorPrimary"
            android:textColor="#FFF"
            android:textAllCaps="false"
            android:minEms="8"
            android:text="Call Method"/>

</FrameLayout>