Points (cashback)

A percentage comes back on every order and is spent on the next one.

Settings → Loyalty. Switch it on, set a percentage (5%, say) and cap how much of an order can be paid with points.

Points are awarded after delivery, not when the order is placed.
A cancelled order awards nothing.
The part paid with points appears in reports «for information», not as an expense.

⚠Points are not an expense: the money did not go out, it never came in. The revenue line is already clear of them, so subtracting them again would count the campaign twice.