On cashless DTU. there are two buttons : Collection and Restock. Every time you refill your vending machine, need press either one to tell the server machine been restocked.
The difference between these two buttons is:
When you press the Restock button, it will put current level of all coils back to Par level.
Collection button will do the same thing, plus, create a collection report which you can see under Collection->History Record menu.