I consulted on this for years, you develop a pretty good sense. It can get oddly arbitrary in some cases, that's for sure, but in most cases it's nowhere near as arbitrary as the dev assumes.

Literally no other client besides Primal has done the most captain obvious thing which is to enable in app-purchase of zaps. (Or at least if one has I've never seen it.) So this talk of mysteries and vagaries to me is like ... what?