Pay button not working on MacBook Air

FWIW the Sequoia 15.7.2 update ushered in some bug fixes, plus an upgrade to Safari 26.1

see > What's new in the updates for macOS Sequoia - Apple Support

and > Update to the latest version of Safari - Apple Support

It comes down to one of three things, the browser isn’t allowing the payment sheet to load, your Wallet data is stuck, or a system process is hung.

To resolve this first try a simple browser switch (Safari to Chrome or vice-versa) to rule out a site-specific script block. Then open System Settings > Wallet & Apple Pay and re-authenticate your card, a stale token often causes silent failures. If that doesn’t move the needle, restart your Mac in Safe Mode, test the same site, and then reboot normally. Safe Mode forces macOS to rebuild caches that commonly break WebKit payment flows. If the button still ignores you, it’s likely a corrupted Wallet plist, removing and re-adding the card fixes it in most cases.

You aren't speaking to Apple here, just other users volunteering their time.

However, this: Apple Pay - Official Apple Support

And if you'd like to describe in detail - without using email or account info - exactly what problem you are having with the MacBook Air, then someone here may be able to offer suggestions.