The district court did not err in holding that Apple violated the UCL’s “unfair” prong by prohibiting app developers from advertising to consumer iPhone users that they could pay through other means than Apple’s in-app payment system and thereby save money. Epic’s mere failure to prove its antitrust claim doesn’t bar it from establishing the practice is unfair under Cal-Tech’s tethered test for suits by competitors or balancing test for suits by consumers. The district court did not err in enjoining this unfair practice. Harm was irreparable because unquantifiable for damage award purposes.