Or just add a clickbait title: "See here to find out if you are eligible to discounted prices!" to a link to the web site.
Of course buyer has to be able to disable the 30% discount on the web site, to make it plausible that the normal prices are the ones on iOS. And all billing lines in the invoice always have to include a 30% discount line on Android and web purchases.
No. You are not allowed to provide customers any details about other payment options. Apple has provisions that basically say, "you must not encourage the user to use a different payment option." And Apple can interpret that quite broadly; telling users that another platform has a discount would be treated as a violation.
> "See here to find out if you are eligible to discounted prices!" to a link to the web site.
This would be a violation of Apple's policies.
I sort of understand why people have a hard time grasping this, and I don't think it's through any fault of their own. It's because it's such an obviously anti-consumer, anti-competitive policy that I think normal people assume "it cannot possibly be the policy that Apple has."
There's almost a defense in audacity: Patreon must be lying about its options because, come on, Apple wouldn't seriously ban links, right? No company would be that bold, right?
The policy is so blatant that people assume there must be something they're misunderstanding about it.