OnPlatform FontFamily breaking Xamarin Previewer Visual Studio

Hello,

I am very new to Xamarin to apologies if this is something obvious. I have a label with the following code -

        <Label Text="Label Text" FontSize="Medium" TextColor="White" Margin="10,0,0,0">
            <Label.FontFamily>
                <OnPlatform x:TypeArguments="x:String"
                            Android="GothamRoundedMedium.ttf#GothamRoundedMedium"
                            iOS="GothamRoundedMedium">
                </OnPlatform>
            </Label.FontFamily>
        </Label>

Now this works perfectly when I run the app and pulls the correct fonts. However, the part that says #GothamRoundedMedium for the android font causes the previewer to give the error "An exception occurred while rendering the control". If I remove that the font no longer works, but the previewer does.

Any help would be much appreciated!