1. Disable Google Pay/Find My Device as Device Administrators in Settings > Security & location > Device Administrators.
2. Search "Google Play services" in the Settings search bar.
3. Press the three dots and press "Uninstall previous updates".
4. Download this update - https://www.apkmirror.com/apk/google...-7-99-release/ Pick your needed edition (arm or arm64, etc.), download it and install it.
5. Disable Background data access for Google Play Services and Google Play in their respective App Info pages.
6. Download Google Pay from the Play Store.
7. Set up your cards. Enjoy!
Never EVER update Google Play services manually, until a Magisk update is available that bypasses the upgraded SafetyNet. Note that Google Play services is responsible for adding/verifying the card, not the Google Pay app! Hence why there seems to be an overlay when adding a card/verifying an existing one.
Tested Google Pay versions:
2.79.x-2.83.235070858 - working
Tested Google Play services versions:
14.7.99 - working
14.8.49-15.0.10 - not working, downgrade to 14.7.99