Honestly, I'm beginning to think that we need some kind of documentation-first style development. Like TDD, but DDD....
I have integrated Facebook APIs, Instagram (well, same thing), Google APIs, Stripe APIs, Mailchimp APIs, etc. etc.
And the only thing common among all of them? The documentation is _terrible_..., like, _terrible_.
I also run a few products online and I spend so, so much time trying to get the documentation right. It's incredibly boring and tedious, but I really feel that if you want to set yourself apart from the big players, make good documentation. It can't be that hard.