He was using a free API that anyone could sign up for.
They did not exchange anything with him. Developing an app to use someone's free API is not an exchange of consideration.
I would never pursue anything further over this app that had about $2,000 of revenue over 10 years. That said, for the record there was consideration.
I had to go through an official approval process that required providing evidence of the app's functionality and a few emails back and forth. I think I actually sent them a prototype of it. And based on that process they decided how many daily API calls to give me. A normal free user did not receive 25,000 API calls per day. I believe if you didn't go through approval back then you got something like 1,000 per month. So there was a consideration process on their part and a determination to green light my use case.
You could argue that the indefinite API access was in exchange for writing the app (service for service), but if this were me, I probably wouldn't bother. Maybe I'd write an adversarial-interoperability backend to replace the API, or open-source the app to allow other interested parties to do so. Or maybe I'd just say "It was a nice run", and let it die.
If you care enough to send a polite email, you could say that Yelp has a prior agreement, you'd appreciate them not reneging, and if they do, you'd appreciate compensation for your labour (minus, of course, the money you made from the software). Probably won't go anywhere, but…
But at that point it’s not a question of cost, it’s a question of how much of your time and headache you want to spend. So yeah, probably not worth it
granting API access in excess of the free tier would most likely constitute something of value, but yeah - probably wouldn't bother, it would be expensive to pursue and not worth it.
> To my mind the acquiring and delivering of the [used chocolate bar] wrappers was certainly part of the consideration in these cases, and I see no good reason for drawing a distinction between these and other cases. — Lord Reid
> It is said that when received the wrappers are of no value to Nestlé’s. This I would have thought irrelevant. A contracting party can stipulate for what consideration he chooses. A peppercorn does not cease to be good consideration if it is established that the promisee does not like pepper and will throw away the corn. — Lord Somervell of Harrow