Text to speech Android studio- Kotlin Doesn't work

I want my application to say a voice message when I press the button "btnObjectDetection". The application does an object detection task, and I want a welcome message. Currently, the application compiles and runs without problem but does not say anything from the voice message. Please help me :( This is my code:

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:app="http://schemas.android.com/apk/res-auto"
   xmlns:tools="http://schemas.android.com/tools"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:background="@color/black"
   tools:context=".MainActivity">

   <Button
       android:id="@+id/btnObjectDetection"
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:onClick="btnObjectDetection_click"
       android:text="Detectar objetos"
       app:layout_constraintBottom_toBottomOf="parent"
       app:layout_constraintEnd_toEndOf="parent"
       app:layout_constraintStart_toStartOf="parent"
       app:layout_constraintTop_toTopOf="parent" />


</androidx.constraintlayout.widget.ConstraintLayout>

MainActivity.kt

import android.content.Intent
import android.os.Bundle
import android.speech.tts.TextToSpeech
import android.view.View
import androidx.appcompat.app.AppCompatActivity
import android.util.Log
import kotlinx.android.synthetic.main.activity_main.*
import java.util.*

class MainActivity : AppCompatActivity(),TextToSpeech.OnInitListener{

    private var tts: TextToSpeech? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        tts = TextToSpeech(this, this)


    }

    override fun onInit(status: Int) {

        if (status == TextToSpeech.SUCCESS) {
            // set US English as language for tts
            val result = tts!!.setLanguage(Locale.US)

            if (result == TextToSpeech.LANG_MISSING_DATA || result == TextToSpeech.LANG_NOT_SUPPORTED) {
                Log.e("TTS","The Language specified is not supported!")
            } else {
                btnObjectDetection.isEnabled = true
            }

        } else {
            Log.e("TTS", "Initilization Failed!")
        }

    }

    private fun speakOut(text: String) {
        tts!!.speak(text, TextToSpeech.QUEUE_FLUSH, null,"")
    }

    public override fun onDestroy() {
        // Shutdown TTS
        if (tts != null) {
            tts!!.stop()
            tts!!.shutdown()
        }
        super.onDestroy()
    }
    fun btnObjectDetection_click(view: View) {
        val intent = Intent(this, ObjectDetection::class.java)
        startActivity(intent)
        speakOut("Welcome to my app! Let's detect objects")

    }


    external fun stringFromJNI(): String

    companion object {
        // Used to load the 'native-lib' library on application startup.
        init {
            System.loadLibrary("native-lib")
        }
    }
}

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.myapp">

    <uses-feature android:name="android.hardware.camera" />
    <uses-permission android:name="android.permission.CAMERA" />
    <uses-permission android:name="android.permission.RECORD_AUDIO" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />


    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.MyApp">
        <activity android:name=".ObjectDetection"></activity>
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

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