Is macOS completely up to date? Are you running a supported version of macOS (10.15.x, 11.x, 12.x)? Older versions of macOS may no longer be considered secure for the Apple Pay feature.
Did you lower or even disable any macOS security settings? If so, it may prevent Apple Pay from working.
Are you using any third party software that is interfering with the normal operation of macOS such as anti-virus software, cleaning apps, or third party security software?
I don't use Apple Pay on the computer, so all of this is just my best guess since I did encounter an issue once about security not being fully enabled which prevented the use of some macOS feature (either macOS was not fully up to date, or I had to disable the option for booting from USB).
Apple Pay is not available for all regions. I also believe Apple Pay only works with Safari.
Use Apple Pay on your Mac - Apple Support
https://macreports.com/apple-pay-disabled-on-mac-because-security-settings-were-modified-fix/