Dialogflow textToSpeech fulfilment not reading aloud the text - dialogflow-es

Question

I am providing users with a response on an audio only device (e.g. google home), when I respond with a textToSpeech field within a simpleResponse, the speech is not read out in the simulator.
Has anyone experienced this and know how to fix?
I've tried different response types but none of them read out the textToSpeech field.
Also tried ticking/unticking end conversation toggle in Dialogflow and expectUserInput true/false when responding with JSON to no avail.
The response is currently fulfilled by a webhook which responds with JSON v2 fulfilment blob and the simulator receives the response with no errors but does not read it out.
RESPONSE -
{
"payload": {
"google": {
"expectUserResponse": true,
"richResponse": {
"items": [
{
"simpleResponse": {
"textToSpeech": "Here are the 3 closest restaurants that match your criteria,"
}
}
]
}
}
}
}
REQUEST -
{
"responseId": "404f3b65-73a5-47db-9c17-0fc8b31560a5",
"queryResult": {
"queryText": "actions_intent_NEW_SURFACE",
"parameters": {},
"allRequiredParamsPresent": true,
"outputContexts": [
{
"name": "projects/my-project/agent/sessions/sessionId/contexts/findrestaurantswithcuisineandlocation-followup",
"lifespanCount": 98,
"parameters": {
"location.original": "Shoreditch",
"cuisine.original": "international",
"cuisine": "International",
"location": {
"subadmin-area": "Shoreditch",
"subadmin-area.original": "Shoreditch",
"subadmin-area.object": {}
}
}
},
{
"name": "projects/my-project/agent/sessions/sessionId/contexts/actions_capability_account_linking"
},
{
"name": "projects/my-project/agent/sessions/sessionId/contexts/actions_capability_audio_output"
},
{
"name": "projects/my-project/agent/sessions/sessionId/contexts/google_assistant_input_type_voice"
},
{
"name": "projects/my-project/agent/sessions/sessionId/contexts/actions_capability_media_response_audio"
},
{
"name": "projects/my-project/agent/sessions/sessionId/contexts/actions_intent_new_surface",
"parameters": {
"text": "no",
"NEW_SURFACE": {
"#type": "type.googleapis.com/google.actions.v2.NewSurfaceValue",
"status": "CANCELLED"
}
}
}
],
"intent": {
"name": "projects/my-project/agent/intents/0baefc9d-689c-4c33-b2b8-4e130f626de1",
"displayName": "Send restaurants to mobile"
},
"intentDetectionConfidence": 1,
"languageCode": "en-us"
},
"originalDetectIntentRequest": {
"source": "google",
"version": "2",
"payload": {
"isInSandbox": true,
"surface": {
"capabilities": [
{
"name": "actions.capability.AUDIO_OUTPUT"
},
{
"name": "actions.capability.MEDIA_RESPONSE_AUDIO"
},
{
"name": "actions.capability.ACCOUNT_LINKING"
}
]
},
"requestType": "SIMULATOR",
"inputs": [
{
"rawInputs": [
{
"query": "no",
"inputType": "VOICE"
}
],
"arguments": [
{
"extension": {
"#type": "type.googleapis.com/google.actions.v2.NewSurfaceValue",
"status": "CANCELLED"
},
"name": "NEW_SURFACE"
},
{
"rawText": "no",
"textValue": "no",
"name": "text"
}
],
"intent": "actions.intent.NEW_SURFACE"
}
],
"user": {
"userStorage": "{\"data\":{}}",
"lastSeen": "2019-04-12T14:31:23Z",
"locale": "en-US",
"userId": "userID"
},
"conversation": {
"conversationId": "sessionId",
"type": "ACTIVE",
"conversationToken": "[\"defaultwelcomeintent-followup\",\"findrestaurantswithcuisineandlocation-followup\",\"findrestaurantswithcuisineandlocation-followup-2\"]"
},
"availableSurfaces": [
{
"capabilities": [
{
"name": "actions.capability.AUDIO_OUTPUT"
},
{
"name": "actions.capability.SCREEN_OUTPUT"
},
{
"name": "actions.capability.WEB_BROWSER"
}
]
}
]
}
},
"session": "projects/my-project/agent/sessions/sessionId"
}
I expect the simulator to read out the result of textToSpeech but currently does not.