Using FAB.forms ?

I am trying to add a Flating Action Button to a simple listview using FAB.forms but nothing is appearing & there are no build errors.

I have added FAB.forms v2.1.1 to a XAmarin Forms PCL project and also added Xamarin.Android.Support.Design to Android Packages.

Following the provided guides I have constructed my XAML page as follows

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:FABTest"
             xmlns:fab="clr-namespace:FAB.Forms;assembly=FAB.Forms"
             x:Class="FABTest.Contacts" >
  <ContentPage.Content>
        <RelativeLayout>
            <ContentView
                RelativeLayout.WidthConstraint="{ConstraintExpression Type=RelativeToParent, Property=Width, Factor=1, Constant=10}"
                RelativeLayout.HeightConstraint="{ConstraintExpression Type=RelativeToParent, Property=Height, Factor=1, Constant=10}">
    <ListView x:Name="EndpointListView" ItemsSource="{Binding Items}" IsVisible="{Binding IsListVisible}" HasUnevenRows="True" SeparatorColor="{DynamicResource ListViewSeparatorColor}" >
      <ListView.ItemTemplate>
        <DataTemplate>
            <ViewCell>
                <Label Text="{Binding Name}" />
            </ViewCell>
        </DataTemplate>
      </ListView.ItemTemplate>
    </ListView>
  </ContentView>
            <fab:FloatingActionButton
                x:Name="fabBtn"
                Source="plus.png"
                Size="Normal"
                Clicked="Handle_FabClicked"
                NormalColor="Green"
                RippleColor="Red"
                RelativeLayout.XConstraint="{ConstraintExpression Type=RelativeToParent, Property=Width, Factor=-50}"
                RelativeLayout.YConstraint="{ConstraintExpression Type=RelativeToParent, Property=Height, Factor=-50}" />
        </RelativeLayout>
    </ContentPage.Content>
</ContentPage>

Are there other additional packages I should be using to get this working?