why not iphone 5s?
I have an Apple Watch that works brilliantly with my small and compact 5s. Why in the world am i precluded from using apple pay on this device combination?
Apple Watch, iOS 8.4, paired with iPhone 5s
You can use Apple Pay on the Apple Watch when paired with an iPhone 5 or later. You can't however, use Apple Pay on the 5s directly since it lacks the necessary hardware (secure element & NFC chip). Of course, your regions need to be set to US (UK sometime this month) to setup Apple Pay.