How to get cloud based styling working in Android

Question

I have followed the instructions here https://developers.google.com/maps/documentation/get-map-id to associate my SupportMapFragment with the cloud based styling. However, nothing happens when I run the app. It's the same default map style. What am I missing?

So, I have the SupportMapFragment set up like this:

<fragment xmlns:map="http://schemas.android.com/apk/res-auto"
        class="com.google.android.gms.maps.SupportMapFragment"
        android:id="@+id/map"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        map:mapId="@string/mapId"/>

And the map ID is in strings.xml.