As far as I can tell the W3C Payments API standardises the path from payment provider to merchant, but the customer to payment provider interaction is the proprietary part.

I.e as a merchant I can easily integrate Apple Pay as an available payment option in the same way as others, but as a customer I can't use Apple Pay unless I'm using Apple sanctioned devices/software and have an Apple account. Other commenters mentioned it only working in Safari, and according to Wikipedia it only works on Apple devices.

You can only use Apple Pay in Safari. But if you use the standard W3C Payments API, a Chrome browser running on an Android device with suitable security will use Android Pay just like an Apple device running Safari will use Apple Pay.

Apple Pay is Safari’s implementation of the standard. Apple stores your payment information and uses the Secure Enclave for authorization. How could Apple ensure a secure path on non Apple browsers or on non Apple hardware?

What’s the use case where you would use Apple Pay as opposed to your hardware vendors implementation on a non Apple device?

Just a snippet from the standard.

https://www.w3.org/TR/payment-request/

This specification standardizes an API to allow merchants (i.e. web sites selling physical or digital goods) to utilize one or more payment methods with minimal integration. User agents (e.g., browsers) facilitate the payment flow between merchant and user.

Ah, I see. So if a merchant supports paying with Apple Pay, they also support paying with Android, or any other payment provider that supports the same standard?

Not automatically. If a merchant does the work to support Apple Pay they don’t get Google Pay “for free”. But if you’ve done the work for Apple Pay, you’ve covered a lot of the ground necessary to support Google Pay, for example.

So they will only support Apple Pay?

Yes.

> I.e as a merchant I can easily integrate Apple Pay as an available payment option in the same way as others, but as a customer I can't use Apple Pay unless I'm using Apple sanctioned devices/software and have an Apple account. Other commenters mentioned it only working in Safari, and according to Wikipedia it only works on Apple devices.

Yeah. It is called the Apple ecosystem. Don't like it? Don't use it. I personally have been very satisfied with Apple so far.

Think of Apple Pay like a virtual credit card.

And so you can't use it without being an account holder just like with Mastercard or Visa.