No heartbeat with serial connection

Hi All,
I’m newbie to px4 and I would be really appreciate for help in next problem.
If I connect px4 via serial port QGroundControl give the error message - “There is a MAVLink Version or Baud Rate Mismatch. Please check if the baud rates of QGroundControl and your autopilot are the same.”
If I try redirect data with mavproxy: --master /dev/ttyUSB0,57600 --out udp:,
I see that there are no hertbeat message from px4. If I use usb connection all works
Please give me some tips of how to connect px4 via serial port.

Did you turn on Mavlink 2.0? If so QGC doesn’t support it yet.