One vector is if you pay in the app, Apple gets its cut.

Platforms that are "mobile first" are at a disadvantage (I'm not sure what Hey's split is).

But in your list, a desktop web UI is primary, and billing can happen there without addition costs. If a company wants to offer payment natively and via an iOS app, Apple gets their 30% on the mobile payments.

So what you're saying is as Microsoft (as an example) does not let you signup/pay for Outlook Premium within the Outlook iOS app Apple do not get a cut?

If so why is this approach being denied to Hey.com? Reading David's tweet it seems Apple are saying Hey.com have to add an option to subscribe and pay for the Hey service within the app and give Apple a 30% cut. Or am I not reading things right?

Edit: further reading shows Apple are comparing "business services" and "consumer" products as being the difference.

As in a "business service" can charge externally to the App Store and provide an app for said service without Apple getting a cut but as a "consumer" that exception is void.

Not really sure how that makes any difference though as Microsoft (again as an example) allow anyone to buy their services be it a business or a consumer. I don't see how this is any different for Hey.com.

I'm not suggesting that Apple applies its policies uniformly, nor that Apple's economics are good nor bad. A company like Microsoft has leverage that Hey does not, and that may be a problem.