How to populate a picker depending on a choice from another picker?

My problem is that I've got a picker and it is not populating when I choose an option on another picker. I have looked at multiple solutions but non is working.

XAML:

            <Picker x:Name="customerPicker" 
                    Title="Customer" 
                    ItemsSource="{Binding CustomerSource}"
                    SelectedItem="{Binding SelectedCustomer}" 
                    Grid.Row="0" Grid.Column="1" />
            <Picker x:Name="salerOrderPicker"  
                    Title="Sales Order" 
                    ItemsSource="{Binding BuildSalesOrderSource}"
                    SelectedItem="{Binding SelectedSalesOrder}"
                    Grid.Row="0" Grid.Column="1" />

This is my XAML code for my Pickers. The first picker is populating.

ViewModel Code:

public List<string> CustomerSource { get; set; }
public List<string> BuildSalesOrderSource { get; set; }

Declaring my Lists for the pickers

private void GetSQLBuildCustomer()
        {
            try
            {
                var customerList = new List<string>();
                using (SqlConnection connection = new SqlConnection(connectionString))
                {
                    connection.Open();

                    using (SqlCommand command = new SqlCommand("SELECT CardCode, CardName FROM OCRD WHERE CardCode LIKE " +
                        "'FOR001' OR CardCode LIKE '115638'", connection))
                    {
                        using (SqlDataReader reader = command.ExecuteReader())
                        {
                            if (reader != null)
                            {
                                while (reader.Read())
                                {
                                    if (reader["CardName"] != DBNull.Value)
                                    {
                                        customerList.Add(new Item(reader.GetString(0), reader.GetString(1)).ToString());
                                    }
                                }
                                CustomerSource = customerList;
                                //Application.Current.MainPage.BindingContext = CustomerSource;
                            }
                        }
                    }
                    connection.Close();
                }
            }
            catch (Exception ex)
            {
                Application.Current.MainPage.DisplayAlert("Alert", "Error Customer Selection lists :" + ex.Message, "OK");
            }
        }

This is to populate the first picker. This piece of code works and populates the picker

    public string selectedCustomer;
    public string SelectedCustomer
    {
        get { return selectedCustomer; }
        set
        {
            selectedCustomer = value;
            OnPropertyChanged("SelectedCustomer");
         
            if (selectedCustomer != null)
            {
                GetSQLBuildSalesOrders(selectedCustomer);
                Static_Var.Changed = true;
            }
        }
    }

This is when I select an option in the first picker and is working

    private void GetSQLBuildSalesOrders(string sCustomer)
    {
        
        try
        {
            var salesOrderList = new List<string>();
            salesOrderList.Clear();
            string Customer = string.Empty;

            using (SqlConnection connection = new SqlConnection(connectionString))
            {
                connection.Open();

                if (selectedCustomer != "")
                {
                    string[] CustomerName = selectedCustomer.Split(':');
                    Customer = CustomerName[0];
                }

                string SQL = "";
                if (Customer.ToUpper().Contains("FOR001"))
                {
                    SQL = "SELECT TOP 1 DocNum, O.[DocEntry],R.[DocEntry], R.Dscription FROM [ORDR] O " +
                       "INNER JOIN RDR1 R ON O.DocEntry = R.DocEntry " +
                       "WHERE [CardCode] = '" + Customer + "' AND [DocStatus] = 'O'";
                        //" AND Cast(O.DocDate as date) = Cast(Getdate() as Date)";
                }
                else
                {
                    SQL = "SELECT TOP 5 DocNum, O.[DocEntry],R.[DocEntry], R.Dscription FROM [ORDR] O " +
                      "INNER JOIN RDR1 R ON O.DocEntry = R.DocEntry " +
                      "WHERE [CardCode] = '" + Customer + "' AND [DocStatus] = 'O'";
                }

                using (SqlCommand command = new SqlCommand(SQL, connection))
                {
                    using (SqlDataReader reader = command.ExecuteReader())
                    {
                        if (reader != null)
                        {
                            while (reader.Read())
                            {
                                salesOrderList.Add(reader.GetInt32(0).ToString() + " : " + reader.GetString(3));
                                DocEntrySelected = reader.GetInt32(1);
                            }
                            BuildSalesOrderSource = salesOrderList;
                            //Application.Current.MainPage.BindingContext = BuildSalesOrderSource;
                        }
                    }
                }
                connection.Close();
            }
           //BuildSalesOrderSource.Add(" ");
        }
        catch (Exception ex)
        {
            Application.Current.MainPage.DisplayAlert("Alert", "Error Creating Orders Selection lists for selected Customer: "
                + ex.Message, "OK");
        }
    }

This is the second picker which is not updating it populate the list but does not display anything.

Thanks for your help.

Please change the type of the BuildSalesOrderSource from List<string> to ObservableCollection<string>.

In other words, you can replace the following code:

public List<string> BuildSalesOrderSource { get; set; }

with code:

public ObservableCollection<string> BuildSalesOrderSource { get; set; } = new ObservableCollection<string>();