Each one is a service that passes its tests and still fails in production. Pick one.
Config values change with no deploy. The visible tests pass. Work out what production does that the tests do not.
One customer's checkout must never change what another customer pays.
The shop's default settings never change while it runs.
Members ship free and get 60-day returns. Everyone else pays shipping under $75 and gets 30-day returns.
Checkouts that happen at the same time must not affect each other.