Hello everybody!
So I decided to prepare a plugin according to your , gba and GJC tips. Dummy payment plugin. With only one php file containing only one function:
function plgVmOnPaymentResponseReceived( &$virtuemart_order_id, &$html) {
if (!class_exists ('VirtueMartModelOrders')) {
require(JPATH_VM_ADMINISTRATOR . DS . 'models' . DS . 'orders.php');
}
$jinput = JFactory::getApplication()->input;
$statusy = array( 'P' => 'oczekujący', 'U' => 'potwierdzony przez użytkownika', 'C' => 'potwierdzony', 'S' => 'wysłany','X' => 'anulowany','R' => 'zwrócony');
$return = $jinput->getArray(array( 'on' => '', 'os' => ''));
$model = VmModel::getModel('orders');
.....
and - URL status change works! Also sends email to me everytime it happens.
BUT

I missed sth, since PLugin interrupts "VM payments method edit page" - FOR EXAMPLE:
With plugin enabled:
/administrator/index.php?option=com_virtuemart&view=paymentmethod&task=edit&cid[]=7
is blank.
With plugin disabled - is ok.
What is wrong? Does payment plugin need some another file, config, language? More plugin must-be functions?
@GJC maybe this is the reason:
you could set its filter to some extra high cart amount so it doesn't show on the frontend
This is my first approach to this topic, since I only desired to manipulate order status - not to have any new payment created .
Regards!