Kotlin ChatApp doesnt show messages - firebase

Question

I simply followed this video: https://www.youtube.com/watch?v=8Pv96bvBJL4&ab_channel=GeeksforGeeks
Untill the end it was working fine. At the end, chat application started to crash when you try to text someone. I simply added push() method.
Now it stopped crashing but I am not able to see the messages. Firebase`s database is perfectly fine but I couldnt make it seen in the app. Sorry for the inexperience. I am new in Kotlin and this is the first time I am a asking a question. Thanks for all of the support.
Here is the code of Chat Activity (In my opinion messageList never adds a thing.. So messages arent showed in the app. But added to database perfectly):
package com.biointel.biointelchatapplication
import android.content.Intent
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.EditText
import android.widget.ImageView
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import com.google.firebase.auth.FirebaseAuth
import com.google.firebase.database.*
import com.google.firebase.ktx.Firebase
class ChatActivity : AppCompatActivity() {
private lateinit var chatRecyclerView: RecyclerView
private lateinit var messageBox: EditText
private lateinit var sendButton: ImageView
private lateinit var messageAdapter: MessageAdapter
private lateinit var messageList: ArrayList<Message>
private lateinit var mDbRef: DatabaseReference
var receiverRoom: String? = null
var senderRoom: String? = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_chat)
val name = intent.getStringExtra("name")
val receiverUid = intent.getStringExtra("uid")
val senderUid = FirebaseAuth.getInstance().currentUser?.uid
mDbRef = FirebaseDatabase.getInstance().getReference()
senderRoom = receiverUid + senderUid
receiverRoom = senderUid + receiverUid
supportActionBar?.title = name
chatRecyclerView = findViewById(R.id.chatRecyclerView)
messageBox = findViewById(R.id.messageBox)
sendButton = findViewById(R.id.sentButton)
messageList = ArrayList()
messageAdapter = MessageAdapter(this,messageList)
chatRecyclerView.layoutManager = LinearLayoutManager(this)
chatRecyclerView.adapter = messageAdapter
// Logic for adding to recyclerView
mDbRef.child("chats").child(senderRoom!!).child("messages").push()
.addValueEventListener(object: ValueEventListener{
override fun onDataChange(snapshot: DataSnapshot) {
//messageList.clear()
for(postSnapshot in snapshot.children){
val message = postSnapshot.getValue(Message::class.java)
messageList.add(message!!)
}
messageAdapter.notifyDataSetChanged()
}
override fun onCancelled(error: DatabaseError) {
}
})
sendButton.setOnClickListener{
// adding the message to database
val message = messageBox.text.toString()
val messageObject = Message(message, senderUid)
mDbRef.child("chats").child(senderRoom!!).child("messages")
.setValue(messageObject).addOnSuccessListener {
mDbRef.child("chats").child(receiverRoom!!).child("messages")
.setValue(messageObject)
}
messageBox.setText("")
}
}
}