I think I should clarify what changed in the rules. Apple attempted to stop any mass communication to your users from mentioning another way to pay. If they signed up in the app Apple still wanted to lock them in as an IAP customer.
Now you can send bulk emails to consenting account holders and mention non-IAP payment methods without running afoul of the rules.
> 3.1.3 Other Purchase Methods: The following apps may use purchase methods other than in-app purchase. Apps in this section cannot, either within the app or through communications sent to points of contact obtained from account registration within the app (like email or text), encourage users to use a purchasing method other than in-app purchase.
That's been changed to:
> 3.1.3 Other Purchase Methods: The following apps may use purchase methods other than in-app purchase. Apps in this section cannot, within the app, encourage users to use a purchasing method other than in-app purchase. Developers cannot use information obtained within the app to target individual users outside of the app to use purchasing methods other than in-app purchase (such as sending an individual user an email about other purchasing methods after that individual signs up for an account within the app). Developers can send communications outside of the app to their user base about purchasing methods other than in-app purchase.
Then the AFAIK unchanged exceptions follow: "reader" (any content store), multiplatform services (yes the guidelines are made so strict allowing the use of previously purchased accounts had to be an exception, "provided those items are also available as in-app purchases within the app"), P2P, "goods and services outside the app", etc.
Now you can send bulk emails to consenting account holders and mention non-IAP payment methods without running afoul of the rules.
Here's the old App Review Guideline clause (https://web.archive.org/web/20210401043354/https://developer...):
> 3.1.3 Other Purchase Methods: The following apps may use purchase methods other than in-app purchase. Apps in this section cannot, either within the app or through communications sent to points of contact obtained from account registration within the app (like email or text), encourage users to use a purchasing method other than in-app purchase.
That's been changed to:
> 3.1.3 Other Purchase Methods: The following apps may use purchase methods other than in-app purchase. Apps in this section cannot, within the app, encourage users to use a purchasing method other than in-app purchase. Developers cannot use information obtained within the app to target individual users outside of the app to use purchasing methods other than in-app purchase (such as sending an individual user an email about other purchasing methods after that individual signs up for an account within the app). Developers can send communications outside of the app to their user base about purchasing methods other than in-app purchase.
Then the AFAIK unchanged exceptions follow: "reader" (any content store), multiplatform services (yes the guidelines are made so strict allowing the use of previously purchased accounts had to be an exception, "provided those items are also available as in-app purchases within the app"), P2P, "goods and services outside the app", etc.
edit: line breaks :)