One is by tracking outgoing links via a specific framework that needs to be used, the ruling only provides for Apple having to allow linking out, no restrictions on Apple’s part for requiring a certain way of doing it.
The other is the courts explicitly affirming Apple’s right to audit as a part of them stating that the commission will still be owed regardless.
The latter is important because it allows Apple to claim a legitimate interest in defense if somehow a case is brought specifically about Apple’s requirements on how to link to a URL outside the app.
Think: “Judge you said the commission would still be owed and you stated we can audit, you even lamented on how cumbersome it would be for all parties involved to settle the commission owed to us if third party payment options would be used, us requiring a specific framework to be used to link outside the app alleviates some of that. We have a legitimate interest in imposing these requirements because it helps us measure links to external purchase flows, which in turn helps us automate measuring these external transactions.”
If you read the appellate court’s judgment, the annoyance towards the district court is palpable. Because the district court both stated the unlawfulness of the anti-steering provision under California statutes as well as stating how cumbersome after the fact collection is of the commission as well as stating that the commission is still owed.
All of this is marginally contradictory, but because the district court didn’t err in sufficient ways for the appellate court to step in and all of it ultimately is in line with the law and standing jurisprudence, the appellate court’s hands were tied, because the appellate court isn’t for do-overs, it’s merely there for significant errors that cause harm.
SCOTUS refused to take up the case, so until further notice the law of the land is that a) developers are allowed to steer users away from the the app while b) Apple remains entitled to their commission regardless because c) there's nothing inherently illegal about Apple's commission because d) it primarily is a payment mechanism for usage of Apple's IP by virtue of how it's structured in the developer agreement and e) as such it's legal because Apple can't be forced to give away their IP for free.