Apple restricts in app Zaps, because they can't take a cut.
So lots of iOS apps don't have zaps in such a way that it's intuitive for us bitcoiners..
Why and how Primal does this differently witht the Apple Guidelines, I don't know exactly. But all other clients are dealing with the same issue.
https://9to5mac.com/2023/06/14/apple-damus-app-store-bitcoin/
You can create your own solution to connect a "like" with a "zap" using NWC. Not optimal, but it's something..
https://www.zapplepay.com/
Other clients with Nostr Wallet Connect may be able to solve this similarly, it's already on a lot of places outside the Apple fences: https://nwc.dev/