Problem with GPS inject and Dragonlink v3

Hi all, I am trying to use GPS inject function of Mission Planner with Dragonlink v3. However, my GPS status keep changing between RTK float and 3D fix, I’ve never got RTK fix result.
I’m using Mission Planner 1.3.46. Dragonlink is configured as instructed in this link: My RTK set is Here+ RTK.
I can get RTK fix result with GPS inject function by connecting USB cable from my laptop to Pixhawk, so I guess the problem is not on the Mission Planner or Here+'s side. Also, I can get params from Pixhawk and control the motors throught Dragonlink, but sometimes the flight data in MP is not updated. Any ideas? Please help.

For better understanding , explain how you have connected here+ ground module with Dragonlink transmitter .?