As fred said, monthly fee. Keep in mind nFusz tech
Post# of 32642
Some ways make more sense than others depending on the situation. For example, if you partnered with GoFundMe to over nFusz tech to all their users for free, then a percentage charge back to GoFundMe would make sense.
These are interesting use cases. If GoFundMe could drive donations say 10% higher using nFusz tech, why wouldn't they pay a royalty to do so.