Android InCallService Dialer Replacement - Loudspeaker not working

Question

i have implemented the IncallService dialer replacement with my own UI and trying to add the basic dialer functionalities. Most of them ( Mute , Play DTMF , Hold) work except setting loud speaker. i tried the below but getting a error "do not have using speaker authority in call". I'm checking on both android 7 and 8 phones.

permission added :"android.permission.MODIFY_AUDIO_SETTINGS"

               val audioManager = 
                applicationContext.getSystemService(Context.AUDIO_SERVICE) as AudioManager
                    // get original mode
                    val originalMode = audioManager.mode
                    audioManager.mode = AudioManager.MODE_IN_CALL
                // change mute
                    val state = !audioManager.isSpeakerphoneOn
               // Loggable.log.debug(LOG_TAG, "Speaker state is  " + state)
                    audioManager.isSpeakerphoneOn = state
                    // set mode back
                   audioManager.mode = originalMode