To clarify a couple of comment above, while App Clips can’t use In App Purchase (that is, StoreKit), they can use Apple Pay to enable payments from within the App Clip. (For example, to buy a smoothie, or unlock a bike.)
See the Streamlined section of
Introducing App Clips, and the
App Clips WWDC20 sessions.
The goal of App Clips is to provide customers quick, easy, and free entry into your app (that they don’t already have installed).