Change to value of Property in ViewModel is not displayed in bound Label on UI

[tradegear]

Trying to do something that would seem basic. I'm probably missing an attribute setting.
The issue is that in code I change the value of a property within a ViewModel, and I'd expect that to be reflect within the UI. It does not. I'm clearly starting from the basics here. I'm starting from the bootstrap bot project in a fresh Maui app, then piecing extracts and snippets from hours of Montemagno's youtube videos and code samples. I've tried to copy the pertinent code snippets and removed unimportant stuff.

MainPage.xaml:

<ScrollView>
    <VerticalStackLayout
        Spacing="25"
        Padding="30,0"
        VerticalOptions="Center">

        <Entry Placeholder="Enter Device Key"
	        Text="{Binding DeviceKey}"
	        HorizontalOptions="Center"/>

        <Entry Placeholder="Enter Password"
	        Text="{Binding Password}"
	        HorizontalOptions="Center"/>

        <Button Text="Get Session Token"
            Command="{Binding GetCommand}"
            HorizontalOptions="Center"/>

        <Label
            Text="{Binding DeviceKey}"
            SemanticProperties.HeadingLevel="Level1"
            FontSize="20"
            HorizontalOptions="Center" />

    </VerticalStackLayout>
</ScrollView>

-----------------------------------------------

MainPage.xaml.cs:

namespace MTRMauiClient;

public partial class MainPage : ContentPage
{
//int count = 0;

public MainPage(SessionTokenViewModel sessionTokenViewModel)
{
	InitializeComponent();
	BindingContext = sessionTokenViewModel;
}

}

MauiProgram.cs:

using MTRMauiClient.ViewModels;
namespace MTRMauiClient;

public static class MauiProgram
{
public static MauiApp CreateMauiApp()
{
var builder = MauiApp.CreateBuilder();
builder
.UseMauiApp()
.ConfigureFonts(fonts =>
{
fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular");
fonts.AddFont("OpenSans-Semibold.ttf", "OpenSansSemibold");
});

	builder.Services.AddSingleton<MainPage>();
	builder.Services.AddSingleton<SessionTokenViewModel>();
	return builder.Build();
}

}

SessionTokenViewModel.cs:

using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;

namespace MTRMauiClient.ViewModels
{
public partial class SessionTokenViewModel : ObservableObject /* implements INotifyPropertyChanged automatically and lots of other stuff */
{
[ObservableProperty]
private string deviceKey;
[ObservableProperty]
private string password;

    [RelayCommand]
    void Get()
    {
        deviceKey = $"!{deviceKey}!"; 

/* just modify to anything different to prove the ViewModel value changed, so the UI can be validated /
string x = deviceKey;
/ for debugging to make sure deviceKey truly was updated wihtin the ViewModel, and I have confirmed it IS.
Why does this change to this value NOT get reflected within the UI Label where Text="{Binding DeviceKey} ?!?*/
}
}
}

Question:
Why is it that when this code in "Get()" changes the value for deviceKey, the UI is not reflecting the data change?
At first I suspected an Entry Placeholder might not accept an update from code, so I created the
<Label
Text="{Binding Password}"
....
to prove that out. This also does NOT reflect the value change to deviceKey

Thanks!

[powerdude]

you're changing the field, not the property that will raise the event(s). change the code to:

  DeviceKey = $"!{deviceKey}!";

[tradegear]

Thank you! - and may all our problems be this simple.
Between when I posted and your answer, I had also tried:
Text="{Binding DeviceKey, Mode=TwoWay}"
Which (a) didn't solve the problem, and (b) I've just tested - wasn't necessary due to the types of controls I'd guess. But probably something to keep in mind for later.