And OMNY will either accept a tap to pay credit card, a phone with tap to pay (including Apple's express card option, where it works even if your phone is dead), or a prepaid value dedicated OMNY card.
It does not actually run the transaction through the entire way - if a transaction fails, the card info gets placed on a blacklist and that particular NFC device won't receive an instant authorisation next time. Generally speaking, people don't have an easy way to generate lots and lots of fake NFC devices, so this hasn't been a problem for widespread fraud (vs just jumping over the turnstile).
It does not actually run the transaction through the entire way - if a transaction fails, the card info gets placed on a blacklist and that particular NFC device won't receive an instant authorisation next time. Generally speaking, people don't have an easy way to generate lots and lots of fake NFC devices, so this hasn't been a problem for widespread fraud (vs just jumping over the turnstile).