I have tried with the below code for sending a custom chat message to existing chat session but not works.

Chat.INSTANCE.init(this, ZENDESK_CHAT_ACCOUNT_KEY)
findViewById<Button>(R.id.chat_button).setOnClickListener {
       MessagingActivity.builder()
        .withBotAvatarDrawable(R.drawable.ic_klipsch_connect_logo)
        .withToolbarTitle("Live Chat")
        .withBotLabelString("Klipsch")
        .withEngines(ChatEngine.engine())
        .show(it.context)

    val callback = object : ZendeskCallback<Void>(){
        override fun onError(error: ErrorResponse?) {
            Log.d("###","onError ${error?.reason}")
        }
        override fun onSuccess(result: Void?) {
            Log.d("###","onSuccess")
        }
    }
    Handler(Looper.getMainLooper()).postDelayed(Runnable {
        Chat.INSTANCE.providers()?.chatProvider()
            ?.sendChatComment("Hello Alpesh here", callback)
    },10000)