Payment vouchers are generated whenever a payment is applied to an invoice. They can be seen in the Related tab on the Closed Deal:
Brokers can use this to see if the client has paid on their invoice, and if their firm has issued a check. In this case, John Broker knows he is due $12,500 but the brokerage has not yet paid him.
In this case, John Broker can see that he has been paid for this deal.