How do I enable payment on my Apple Account via web?

Have a look at the steps mentioned in this article:

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To use Apple Pay, you need:

• A compatible device with the latest version of iOS or iPadOS, watchOS, macOS, or visionOS.
• A supported card from a participating card issuer.
• An Apple Account signed in to your Apple device.
• Face ID, Touch ID, Optic ID, or a passcode set on your device.

Learn if your country/region supports Apple Pay. To check if your card is compatible with Apple Pay, contact your card issuer.

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Set up Apple Pay - Apple Support

To use Apple Pay online:

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You can use Apple Pay to pay online or in apps when you see Apple Pay as a payment option.1,2

1. Tap the Apple Pay button or choose Apple Pay as your payment method.
2. To use a payment method different from your default card, tap Other Cards & Pay Later Options or Change Payment Method. You can also tap your default card and swipe to view your other cards. 
3. If necessary, enter your billing, shipping, and contact information. 
4. Confirm the payment.

• • iPhone or iPad with Face ID: Double-click the side button, then use Face ID or your passcode.
  • iPhone or iPad without Face ID: Use Touch ID or your passcode. 
  • Apple Vision Pro: Use Optic ID or your passcode.
  • Apple Watch: Double-click the side button.
  • Mac with Touch ID: Place your finger on Touch ID. 
  • Mac without Touch ID: Confirm the payment on your Bluetooth-connected iPhone or Apple Watch. Make sure that you're signed in to the same Apple Account on all devices.

5 . When your payment is successful, you'll see Done and a checkmark on the screen.

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copied from: Make purchases using Apple Pay - Apple Support

Remember, that your banking institution has to support Apple Pay:

Countries and regions that support Apple Pay - Apple Support