How to set enable default action button?

Hello,

I want to enable the button “Enter AP Bill” which associate with action CreateAPInvoice on Purchase Orders screen

by implementing Event handler Row_Selected as following:

protected void POOrder_RowSelected(PXCache cache, PXRowSelectedEventArgs e, PXRowSelected InvokeBaseHandler)
        {
            if (InvokeBaseHandler != null)
                InvokeBaseHandler(cache, e);
            var row = (POOrder)e.Row;
            if (row != null)
            {                
                if (row.Status == POOrderStatus.Hold)
                {
                    Base.createAPInvoice.SetEnabled(true);
                }
            }
        }

but it doesn’t working.

Do you have any suggestion?