start listener

private fun startSMSListener() {

        val client = SmsRetriever.getClient(this /* context */)
        val task = client.startSmsRetriever()
        task.addOnSuccessListener {
            // Successfully started retriever, expect broadcast intent
            // ...
           // otpTxtView.text = "Waiting for the OTP"
            Timber.e("SMS Retriever starts")
        }

        task.addOnFailureListener {
            //otpTxtView.text = "Cannot Start SMS Retriever"
            Timber.e("Cannot Start SMS Retriever")
        }
    }