This was an Apple requirement. They couldn’t get their cut of the zaps! There is a workaround using emoji comments and then automatically zapping from another webapp but the ux isn’t great. Primal uses @strike behind the scenes which I presume gets around the inapp purchase requirements.

No Bullshit Bitcoin

Zapple Pay: Zaps From Any Nostr Client

"Zapple Pay lets you automatically zap notes based on if you give a ⚡ reaction."