Email attachment

Hey Team Enfold!
I add this filter to my function.php to have email attachments for woocomerce order:

add_filter( ‘woocommerce_email_attachments’, ‘my_email_attachments’, 10, 3);
function my_email_attachments ( $attachments , $id, $object ) {

if( $id === ‘customer_completed_order’){

$attachments[] = get_attached_file( 1640 );
$attachments[] = get_attached_file( 1639 );

}

return $attachments;
}

Unfortunately, I doesn’t work at all. What did I do wrong?

BR
Thomas