ContentPage Frame HeightRequest not setting

I am on Xamarin Forms 3.3 deploying to Android 5.0 API 21 and it seems that I cannot set the HeightRequest of the Frame on the content page. I have changed the Frame to StackLayout (this gives me a shorter layout but still no able to set the heightrequest). Where is my mistake? Thank you.

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="MyApp.View.RegistrationPageFour"
             x:Name="Page4ContentPage" >


    <NavigationPage.TitleView>
        <StackLayout Orientation="Horizontal" 
                     VerticalOptions="Center" Spacing="10" >
            <Label Text="Password"  TextColor="White" FontSize="24"  VerticalTextAlignment="Center" />
        </StackLayout>
    </NavigationPage.TitleView> 


        <Frame x:Name="Page4Frame" Padding="0,0,0,0"  HeightRequest="400">
            <FlexLayout x:Name="Page4FlexLayout" Direction="Column" AlignItems="Center" JustifyContent="SpaceEvenly" >
                <StackLayout Padding="10,20,10,50" >
                    <Label Text="Please key a secure password" FontSize="24"/>
                </StackLayout>

                <StackLayout Padding="10,0,10,20" Spacing="15" >
                    <Entry x:Name="Password" Focused="OnPasswordFocused" FontSize="Large" Placeholder="Password" IsPassword="True" MaxLength="64"/>
                    <Entry x:Name="Password2" FontSize="Large" Placeholder="Repeat Password" IsPassword="True" MaxLength="64" />
                </StackLayout>
                <StackLayout>
                <Button Text="Done"  x:Name="Page4Done" 
                        WidthRequest="120"  BorderRadius="60" VerticalOptions="Center" 
                        StyleClass="primary" HorizontalOptions="Center"
                        Clicked="OnButtonClicked" />
                </StackLayout>
        </FlexLayout>
        </Frame>

</ContentPage>