Took me a bit to understand, courier doesn't have the bill, the drop does.
Boss: "Courier, deliver this money to <address>, code is 12345678"
Courier: at <address>, "Hey Drop, what is the code?"
Drop: "Code is 12345678"
Courier: "That's correct, Here's you're money"
Drop: Tears bill in half and hands part with serial number to Courier as proof
Boss: "Courier, deliver this money to <address>, code is 12345678" Courier: at <address>, "Hey Drop, what is the code?" Drop: "Code is 12345678" Courier: "That's correct, Here's you're money" Drop: Tears bill in half and hands part with serial number to Courier as proof