Right now CurrencyManager#getActorCurrencyUpdates only works if you have enough currency of some denomination to fulfill the request, but it isn't capable of making change in order to create the necessary denominations if required. For example, if you have a character with 100 gold and no copper and ask to deduct 20 cp then it will not work. Ideally the system would be able to see that the player doesn't have enough copper to complete the transaction and would be able to convert one of the gold pieces into 100 cp before doing the deduction.