Kotlin - menuInflater cannot find reference of the xml file

I am trying to add create option menu to my activity, however the android-studio sent me this error
Unresolved reference: chat_app_menu
Here is my code in Kotlin

override fun onCreateOptionsMenu(menu: Menu?): Boolean {
        menuInflater.inflate(R.menu.chat_app_menu)
        return true
    }

The line with menuInflater.inflate(R.menu.chat_app_menu) show me the error Unresolved reference: chat_app_menu
However, I have been create the resource file chat_app_menu.xml under res\menu\

Here are my import files

package com.example.chat_app

import android.R
import android.os.Bundle
import android.util.Log
import android.view.Menu
import android.view.MenuInflater
import androidx.appcompat.app.AppCompatActivity
import com.google.firebase.auth.FirebaseAuth

My file directory:

What should I do to disable this error to make the app work?