You can change the credit card, shipping address, or contact information before completing your purchase.
Complete the purchase.
Mac with Touch ID: Place your finger on Touch ID to complete the purchase. If you haven’t set up Touch ID, you can tap the Pay button in the Touch Bar and enter your password. If your Mac doesn’t have a Touch Bar, you can double-tap Touch ID and enter your password.
Only one user account on your Mac can use Touch ID on the Mac to complete purchases with Apple Pay. Other user accounts must use iPhone or Apple Watch.
iPhone: Double-click the side button, then authenticate with iPhone User GuideApple Watch User Guide