In the top of every request, you find the toolbar. This bar changes depending on what stage the request is in. It starts out in its negotiation phase during which you will see the Confirm/ Accept, Edit terms and Decline buttons.
Once a request has been accepted the toolbar will changes so the supplier can provide Release references by clicking Provide Pick-up Details. As a user, you can remind the supplier to provide pick-up details which trigger an email to your partner.
Once all containers are reported as empty returned the request is seen as completed and the toolbar will not show options not available at that point.