Listview button problem

I'm outputting data to a Listview on a page, for each item in the page I assign an 'Id' to a buttons command parameter, taken from a database (part of RModels). I'm trying to bind the button to call the command EditGSM but doesn't appear to do so. If i move the button code outside the Listview it triggers the command fine.

Content Page:

  <ContentPage.BindingContext>
        <vm:GSMUnitsViewModel/>
    </ContentPage.BindingContext>

    <ContentPage.ToolbarItems>
        <ToolbarItem Text="Logout" Command="{Binding LogoutCommand}" Clicked="Logout_Clicked" />
    </ContentPage.ToolbarItems>

    <StackLayout>
        <ListView ItemsSource="{Binding RModels}" HasUnevenRows="True">
            <ListView.ItemTemplate>
                <DataTemplate>
                    <ViewCell>
                        <StackLayout>
                            <Label Text="{Binding IMEI}" />
                            <Label Text="{Binding Description}" />
                            <Label Text="{Binding Model}" />
                            <Label Text="{Binding Created}" />
                            <Button Command="{Binding EditGSM}" CommandParameter="{Binding Id}" Text="Edit GSM" />
                        </StackLayout>
                    </ViewCell>
                </DataTemplate>
            </ListView.ItemTemplate>
        </ListView>
    </StackLayout>

ViewModel:

    public class GSMUnitsViewModel : INotifyPropertyChanged
    {
        ApiServices apiServices = new ApiServices();
        private List<GSMRegModelList> _rmodels;



        public GSMUnitsViewModel()
        {
            Task.Run(async () => RModels = await apiServices.GetGsmUnits(Settings.AccessToken));

        }

        public List<GSMRegModelList> RModels
        {
            get { return _rmodels; }
            set
            {
                _rmodels = value;
                OnPropertyChanged();
            }
        }


        public ICommand EditGSM
        {
            get
            {
                return new Command(() =>
                {
                    var test = "dfdf";
                });
            }
        }


        public ICommand LogoutCommand
        {
            get
            {
                return new Command(() =>
                {
                    Settings.AccessToken = "";
                    Settings.Username = "";
                    Settings.Password = "";
                });
            }

        }

        public event PropertyChangedEventHandler PropertyChanged;

        protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }

    }