How to read mavlink data sent from QGroundControl Station to Ardupilot Using ROS

Hi all! I’ve been trying to listen to mavlink messages sent by GCS(QGroundControl) to Ardupilot(SITL) using a companion computer runninig a ROS node. I am unable to see any messages in rostopic echo /mavlink/to . But I am able to see messages sent from Ardupilot(SITL) using rostopic echo /mavlink/from .
This is the command I used to launch mavros roslaunch mavros apm.launch fcu_url:=udp:// gcs_url:=udp://@ I suspect I am doing something wrong in this. Or is it even possible to read and send mavlink messages from a companion computer.
Thank you.