I can imagine many more models, but there are three elements: The required action infrastructure (for instance creditcard payments); The observation the action occured (for instance the payment provider anouncing a payment happened via a DM); The mutation of the list (for example a bot on the creator side that looks for such dm's before it takes action). The last part always demands something from the content creator because of requirement to sign with particular keys, but where those other two are residing could differ.