The app on your phone act as your key when renting a trailer. Therefore if you forget to open the Bluetooth lock before returning the trailer in the app you won't be able to unlock it. When this happens please contact our customer support, their contact information can be found on the website.
Customer support will then help you re-activate your booking so you can open the Bluetooth lock with the app again. Which will make sure that you can lock the trailer properly before leaving the station.