MVVM Bindings doesnt update with PropertyChanged

Question

All my bindings are not updated and I don't understand why

My Model is:

Public Class TestModel
    Implements INotifyPropertyChanged

    Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged



    Private Sub NotifyProperyChange(ByVal Info As String)
        RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(Info))
    End Sub

    Private m_vorname As String
    Public Property vorname() As String
        Get
            Return m_vorname
        End Get
        Set(ByVal value As String)
            If m_vorname <> value Then
                m_vorname = value
                NotifyProperyChange("vorname")
                MessageBox.Show("Vorname wurde zu:" + m_vorname)
            End If
        End Set
    End Property


    Public Sub wertverandern()
        vorname = "Lukas"
    End Sub
End Class

My View is the MainView with this settings:

Imports System.ComponentModel
Class MainWindow

    Private WithEvents m_Person As New TestModel

    Public Sub New()

        ' Dieser Aufruf ist für den Designer erforderlich.
        InitializeComponent()
        Me.DataContext = New TestModel()

        ' Fügen Sie Initialisierungen nach dem InitializeComponent()-Aufruf hinzu.

    End Sub

    Private Sub btn_Test_Click(sender As Object, e As RoutedEventArgs) Handles btn_Test.Click
        m_Person.vorname = "MOINSEN"
    End Sub

    Private Sub m_Person_PropertyChanged(sender As Object, e As PropertyChangedEventArgs) Handles m_Person.PropertyChanged
        MessageBox.Show("Ausgeloest:" + m_Person.vorname, e.PropertyName)
    End Sub

    Private Sub gelicked(sender As Object, e As RoutedEventArgs) Handles btn_XXX.Click
        m_Person.wertverandern()
    End Sub
End Class

My XAML look like this:

    <Grid>
        <StackPanel Orientation="Horizontal">
        <Button Name="btn_Test" Height="100" Width="100" VerticalAlignment="Center" HorizontalAlignment="Center" Content="1"/>
            <Button Name="btn_XXX" Height="100" Width="100" VerticalAlignment="Center" HorizontalAlignment="Center" Content="{Binding vorname}" Margin="20"/>

            <Label VerticalAlignment="Top" Background="Red" Width="100" Height="40" Foreground="Black" Content="{Binding vorname, FallbackValue=GEHT_NICHT, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
        </StackPanel>
    </Grid>