ApplePay is a popular payment wallet for Apple users available on iOS and on web apps on Apple devices.
So, ApplePay is not a payment method, but a container for credit cards (which are the payment methods).
It needs the integration of a payment processor to register credit cards. In other words, integration work is needed with every payment processor that needs to be supported.
ApplePay provides contactless payments over NFC (near-field communication < 4cm). The service is estimated to be enabled on 51% of iPhones globally or 507 Mio ApplePay users (9/2020). The service is usable anywhere where contactless payments are accepted (US > 75%, UK > 85%, Australia 99% of stores).
ApplePay is PSD2 SCA compliant (strong customer authentication with payment service directive of EU) and supports liability shift for Amex, MC, Visa, JCB, Discover in Europe.
Usage of ApplePay is restricted by Apple to:
Mobile: iOS only (> v11.3)
Web: Safari Desktop 10.0+ and Safari Mobile 10.0+
on iOS devices with a Secure Element — an industry-standard, certified chip designed to store payment information safely.
on macOS, users must have an Apple Pay-capable iPhone or Apple Watch to authorize the payment, or a Mac with Touch ID.