When you are done with the ride, you can finish the ride inside of the virtual station. You can find virtual stations in the map view of the app.
To end the ride in the virtual station, you have to close the back wheel lock and press "END RENT" in the app. You will receive a pop-up confirmation that the bike was successfully returned.
WARNING! The end does not rent, if you just close the lock!
To end the rent, you have to lock the rear lock, and finish the ride in the app. Wait until you receive a pop up msg that the rent has ended successfully.