There should have been an email months ago saying they were converting their API to be paid. Not a 4-day threat to shutoff your API key or pay-up. As I mentioned in my post, I was not aware that they were converting to a paid program and had received no prior emails.

Yes, I got that, but why should they bother? Your understanding is that you were business partners, while in fact, you were just lucky enough to get access to their service for some years.

If you had an actual contract, it would be a different story. Your product would still be not more than some UI to some walled garden, and nothing particularly valuable, but at least you would be officially permitted to do so.

So you basically sold something to Apple users that you don't actually own, and that is completely out of your control, and that was always in danger to just stop working suddenly.

And, on the other hand, I'm sure you've implemented a (for a hobby) decent app, and maybe you actually brought a handful of new visitors to them (which wouldn't have just used their website if your app wouldn't exist). But do you really think that at Yelp they are sitting there and just think how they can return the favor?

They basically think "well, that funny dude has now played enough". You never were a partner for them. Just what people call " useful idi*t" (sorry, but that's just the term ^^) at best. They haven't talked about you at their christmas party!

If you're up front and reasonable, you're more likely to convert developers to pay for the new API. If you do it last minute, not only can't developers make the switch in time, you've lost their trust, making it harder to convince developers to bother investing their time and resources.

It goes both ways.

Btw, he had a contract.