From Samsung.com :
11Samsung Pay is not available on iOS smartphones. After initial setup, Samsung Pay on Galaxy Watch can make at least five transactions without reconnecting to a network. Samsung Pay on Galaxy Watch requires network connection through LTE or Wi-Fi or via Bluetooth pairing with compatible smartphone. Samsung Pay on the Galaxy Watch is only compatible with select cards, carriers, and Samsung devices and non-Samsung Android phones. Samsung Pay on the Galaxy Watch is compatible only with NFC-type payment terminals.