The child safety seat interface (vertical opening) can be found in the rear seat hip position of 1. There is a circular safety seat interface sign next to the opening.
ISOFIX interface for rear seats
There is an optional safety seat binding ring slightly below the seat belt hook. You can usually find it along the seat belt.
Safety seat fixing ring on carriage wall
There is also a binding port in the back seat.
Binding port on the back seat