When a ride is paused, the car locks, and you pay per minute while the ride is paused.
Locking the car
During an active ride, you can press the three-dots button on the right, and the option to pause appears.
Note that the maximum pause is 4 hours, after which the ride is ended immediately. If that happens when you are outside the operating zone you will receive a parking penalty..
Unlocking the car
To unlock the car, press the Unlock button on the bottom of the screen. The doors on the car should unlock automatically.
If you have any issue with locking/unlocking the car, it might be due to connection issues. If you are inside or surrounded by large buildings, try moving the car to a more open area outside.