Why the Apple Pay button is not displayed ?

Apple Pay allows your customers to easily and securely make purchases on your shop, from their Mac, iPhone (iOS 10 or later), or Apple Watch (watchOS 3 or later).

The Apple Pay payment feature is available only in Apple devices and under the Safari browser.

Compatible models with Apple Pay are:

iPhone:

• IPhone models with Face ID
• IPhone models with Touch ID, except iPhone 5s

iPad:

• IPad Pro, iPad Air, iPad and iPad mini models with Touch ID or Face ID

Apple Watch:

• Apple Watch Series 1 and 2 and later models
• Apple Watch (1st generation)

Mac:

• Mac models with Touch ID
• Mac models introduced in 2012 or later with an iPhone or Apple Watch compatible with Apple Pay

Be careful, Apple Pay feature is only available in some countries and some banks, you can find the complete list on the Apple official website.