BindableProperty.CreateAttached() method raises Error on build

I'm pretty new to .NET

In .NET MAUI 9.0 I am creating an app based on a custom Layout extending the Grid class, which uses several BindingProperties that i have no issues with:

namespace krizanke_ux.Resources.LayoutResources
{
    public partial class ParametricGrid : Grid
    {
        public static readonly BindableProperty GridWidthProperty =
            BindableProperty.Create(nameof(GridWidth), typeof(double), typeof(ParametricGrid), 10.0,
                propertyChanged: (b, o, n) => ((ParametricGrid)b).RebuildGrid(),
                validateValue: (b, value) => (double)value >= 0.0);

I've now started implementing attached properties for the Grid's children, which raise the following error: XC0009: No property, BindableProperty, or event found for "GridHorizontalAlignment", or mismatching type between value and property.

Here is the appropriate code:

private static readonly BindableProperty GridHorizontalAlignmentProperty =
    BindableProperty.CreateAttached("GridHorizontalAlignment", 
        typeof(LayoutAlignment), typeof(ParametricGrid), LayoutAlignment.Start);

public static LayoutAlignment GetGridHorizontalAlignment(BindableObject view) =>
    (LayoutAlignment)view.GetValue(GridHorizontalAlignmentProperty);
public static void SetGridHorizontalAlignment(BindableObject view, LayoutAlignment value) =>
    view.SetValue(GridHorizontalAlignmentProperty, value);

<ContentPage ...
             xmlns:layout="clr-namespace:krizanke_ux.Resources.LayoutResources"...>
<layout:ParametricGrid ...>

<Entry
    Grid.Row="5"
    layout:ParametricGrid.GridHorizontalAlignment="Center"
    Grid.RowSpan="4"
    Grid.ColumnSpan="7"/>

I cannot find the solution anywhere. I've tried using both LayoutOptions and LayoutAlignment, using GridHorizontalAlignmen="{x:Static LayoutAlignment.Center}" even though Visual Studio automatically suggests "Center" in XAML.