I'm building an app that uses Alexa's API's. I've noticed that when I view echo devices in the Alexa app I can control the volume of those devices FROM the app.
I would like to expose the same functionality for my app, however when I view my app in the Alexa devices section, even when the app is connected, the volume slider does not show up.
I have have implemented the SpeakerInterface and my app does seem to properly respond when Alexa sends it volume up and volume down requests in response to a speech recognizer request, it just does not show a volume control in the Alexa app.
What are the requirements for this to work or is this an echo device exclusive feature?