Wallet & Apple Pay - Not showing up

your device must have Touch ID enabled.

Mac issues

• Although rare, adding payment cards to Macs can sometimes be an issue. If you are having trouble adding a card to your Mac - on the iPhone go to settings>Wallet & Apple Pay>allow payments on Mac. Your Mac must be signed into the same Apple ID as your iPhone. Your cards should already be added to your Mac if you are signed into both. If you still have issues you can sign out of your Apple ID and back in which usually resolves the issue. Set up Apple Pay - Apple Support
• To use Apple Card for online stores you need the entire card number. Once you use it once your keychain should remember the card number if you choose that option. To get the entire card number go to Wallet>Apple Card>tap the three dots in the circle>tap card information.
• If more troubleshooting needs to be done the following links could be helpful. (About Secure Boot, Reset NVRAM or PRAM on your Mac, How to reset the SMC of your Mac)
• If you created a bootable clone of your device, and booted to it, and enabled FileVault, macOS (Big Sur) may move the Apple Pay authorization to that external drive and disable it on the internal one. The resolution may be to delete one card, which will then trigger a prompt about the disk authorization move, and ask you to reset Apple Pay. Reset Apple Pay, then re-enter the CCV's for all the cards and since you have not rebooted, the error may still be present. Reboot and the system should be fine. (information gathered from another thread update to Big Sur made Apple Pay stop wor… - Apple Community)
• If you are getting a message that "Apple Pay has been disabled because the security settings of this Mac were modified" - go to Software Update/Advanced and uncheck the recheck "Install system data files and security updates." to see if that resolves the issue.