Each feature available in the Apps Engine is mapped to a permission. Adding the permission in the app's manifest (
app.json file) will unlock said feature to be used by the app. For example, if you add "send messages" as a permission in your app's manifest, your app will be able to send messages in the Rocket.Chat server. If your app tries to send a message without having the "send messages" permission listed in the manifest, the Apps Engine will block the feature and the app will not be able to perform the desired action.