Accuracy values always 0 (H_ACC, V_ACC, VEL_ACC)

Hello,

I am trying to read Horizontal Accuracy (H_ACC) online. I already set up MAVLINK2 and I am able to get the extended fields for GPS_RAW_INT (h_acc, v_acc, vel_acc). But the value for these fields is always 0. I checked this using Mission Planner, reading the data with dronekit and wit APM2 and the values for the extended fields are always 0. I get values for number of satellites, Lat, Lon, HDOP, etc, but not for h_acc, v_acc, vel_acc. Can please someone give me a hint.

Thank you in advance!