Bigbug I think we want different things.
If I used the feature you're working on using tokens (as a currency) rather than money and a ticket resulted in an invoice in tokens with pre-purchased tokens being a credit against this invoice, the tokens would have either been provided free or purchased in advance for money, probably in accounting software rather than ITFlow, but possibly in ITFlow.
I don't want to associate tokens with money at the point of consumption. Nor do I want invoice/credit like transactions, just a decrement of tokens. So what I envisage is not like a credit note in money currency as tokens only have a value in time for services and <> money. Tokens are only exchangeable for time and have no monetary value.
I get functionality these are almost the same, by psychologically to the consumer they are not.