elevator system msgs is required.
You need to download interfaces.
Please, refer to here
ros2 run cloisim_ros_elevator_system standalone
ros2 run cloisim_ros_elevator_system standalone --ros-args -p target_model:=SeochoTower -p target_parts_name:=elevator_system
ros2 service call /elevator_system/request_door_open elevator_system_msgs/srv/RequestDoor "{elevator_index: 0}"