Why does joomla 1.5 confirm the order before payment?

Question

Joomla

Got here in the antiquities shop - you need to make a payment plugin for Joomla 1.5. Everything seemed to be done, but then I noticed that the standard payment procedure confirms the order even before the payment is made. Those. after the order confirmation page, regardless of payment completion, the order is already closed. If anyone has come across - tell me: how to make virtuemart wait for a response from the payment system? Thanks to all!