Note: Depending on your company's or organization's partnership with Wunder (click here for more info on this), you might also have the option to perform/receive payments via the app. If that is not the case, please disregard this article, seeing as the fare price will just be automatically locked at 0€ p/ km.
Car owners can decide the share per kilometer they would want to propose to the passenger for the ride. However, the cost share shown to the passenger is calculated for the actual distance of carpool for the passenger with the car owner. This means that you could see different carpool cost share for different matches depending on the amount you have quoted per kilometer and the length of ride overlap between your ride and the passenger's.
Note that this is a suggested price and negotiation from the passenger side should be welcomed - as long as both are happy with the final price.
To change the fare, drivers can go to Settings -> Car Settings -> Price per km.