When the NVC automated system said that AOS fee bill was generated, my wife called the operator to get the invoice number to use it online. and the lady said that the online system is not working at the moment and that it's down because of some bugs.
She almost hung up without the number, but my wife insisted to get it just in case so that we don't have to call again.
Cut the BS. The online system is working perfectly. We used it, status changed to PAID in the next morning.
Just wanted to let you know, so in case you're calling NVC ignore any crap about systems malfunctioning or not working.. the page will not exist on state.gov if it wasn't functioning.