Accelerometer does not the cal

Hello All,
I’m new in this world and sorry for my not best English. I’m writing from Italy.
I’m trying to install an APM 2.8 (bought as new for 20€) on my bait boat to have an autopilot.
At now my 1st issue is that i’m not able to perform the accel cal. At the 1st step, with APM in level position, immediately it returns a failed to perform cal.
I tried to use different firmware for ROVER without positive notice.
But, in the simulation, if I move the APM in all direction it returns a good feedback. The horizon is levelled and also the right, left, up, down movement are correctly shown.
What I can do to perform the cal? I watched a lot of videos on YT but they use all older release of MP.

THX a lot!

The last Ardurover firmware that supported the APM Flight Controller was V2.5 from 2015. So even if it was 0€ A current board would have been a better choice.

Dave this is not the answer I’m waiting for but…I accept your opinion.
As I told I’m not exeprienced in Ardurover and I choose to spend less money as possible to try.
In future I know that I’ve to spend more.
But what I’d like to know is if is possible to do what I want to do? The planner automatically install the latest FW for my board but I don’t know why I’m not able to perform accel cal.
Is possible that the planner can’t do it with my controller?