Mavlink debug message via USB

Dear all,
I wanna send debug message over mavlink to QGC, using: mavlink_msg_statustext_send(MAVLINK_COMM_2, 0, msg), where MAVLINK_COMM_2 stands for the USB port, in px4flow source code. But when I call this function, QGC does not show the message in ‘msg’ of the function. Could anyone give me some advice how to view the message in QGC? Thanks

EDIT: maybe a screenshot is helpful. I do not see where the message shows.