Calibrating accel

hello everyone am new to building with apm, so i got an apm 2.8 i tried many times to calibrate the accelemeter but it takes long and writes calbration failed
(i tried latest version of mission planner and an old one but the same)
Ill be thankfull if someone helps me on this issue

It might work with the Mission Planner version that has the release date overlaps with the firmware version that you have in the apm 2.8.
The best to do is to get a supported board.