But it’s still quite painful to manage the credentials for an application with many APIs. And, relatedly, it’s hard to monetize anything but the most mission critical APIs. That’s because the primary cost of buying an API is often not the per-invocation cost of running the API, which can be in fractions of a cent; instead, it’s the fixed cost in developer time and energy of signing up for it.
Buy 50+ APIs with Bitcoin in the 21 Marketplace

In a world of ‘talking machines’, this should be the default way to pay for all the chatter :)