Connecting to pixhawk orange via mro sik radio transmitter

Hi, I am new to pixhawk and trying to connect to a pixhawk orange flight controller using a MRO sik radio transmitter via MAVROS. Can anyone give instructions on connecting to pixhawk using mavros with ardupilot firmware in it?
I am getting these error messages while using

roslaunch mavros apm.launch

[FATAL] [1676924296.005945001]: FCU: DeviceError:serial:open: No such file or directory
================================================================================REQUIRED process [gs/mavros-2] has died!
process has finished cleanly
log file: /home/jayanth/.ros/log/b4f8eb38-b15b-11ed-979d-5b90a2e40f4b/gs-mavros-2*.log
Initiating shutdown!