The tts format was changed, the title is no longer spoken. All spoken messages are now under tts_text.
media_stream: "alarm_stream" will allow you to specify the alarm channel which will play even if the volume off. Otherwise it will play through the media streamed and can be controlled by the phone’s media volume.
Use this for the data portion of the notification:
{
"message": "TTS",
"data": {
"tts_text": "Motion has been detected",
"media_stream": "alarm_stream"
}
}