Ok, slight change to the above function. Think you have to use the order id rather than the post ID:
function delegate_form_update($value, $order, $field) {
// only do it to certain custom fields
if($field['name'] == 'ticket_alloc') {
// get the old (saved) value
$old_value = get_field('ticket_alloc', $order->get_id());
// get the new (posted) value
$new_value = $_POST['acf']['field_63ca95e88557a'];
// check if the old value is the same as the new value
if($old_value != $new_value) {
// Do something if they are different
} else {
// Do something if they are the same
}
}
// don't forget to return to be saved in the database
return $value;
}
add_filter('acf/update_value', 'delegate_form_update', 10, 3);
