According to the Nostr protocol, on which Damus is based, zaps are simply tips.

Apple’s quibble with the feature is its non-adherence to guideline 3.1.1, which mandates the use of in-app purchases for transactions connected with digital content. Apple is unwavering on this: “We noticed that your app allows users to send ‘tips’ associated with receiving content from digital content creators with a mechanism other than in-app purchase,” the company pointed out.