RadzenDataGridColumn GetOrderIndex always returning null

Have a datagrid with AllowSorting=true, AllowMultiColumnSorting="true", and ShowMultiColumnSortingIndex="true"
I'm handling the grid Sort event as I have to provide sort info to gRPC for actual sorting.
When I iterate the columns the col.GetOrderIndex is always returning null. Am I missing something? Here's a simple loop I was using for testing (would simplify and sort with LINQ for final):
protected async Task HandleSortEvent( DataGridColumnSortEventArgs args)
{

var visibleColumns = grid.ColumnsCollection.Where( 
                                    c => c.GetVisible()).ToList();

foreach (var col in visibleColumns)
{   string? colname = col.Property;
    if (string.IsNullOrEmpty(colname))  continue;
    SortOrder? srtorder = col.GetSortOrder();
    if (col.Sortable && srtorder != null)
    {   int? idx = col.GetOrderIndex(); 
        // at this point idx is always null
        // note: srtorder   - is correct
    }
}

}

OrderIndex is not related to sorting.

Thanks, I used GetOrderIndex instead of GetSortIndex to get the field sort order.