Ubiquiti UAP-AC-Pro-Gen2 fails to install

I used this access point before and openwrt installed fine.
The first step is to downgrade the firmware to 3.7.58.
This new UAP-AC-Pro has the installed version 4.3.31 and it refuses to downgrade.
after I tftp the ubnt-3.7.58.bin firmware the device reboots but still shows 4.3.31.

Is there any tips to force the downgrade?

I also tried to copy mtd and the libc onto the device, but this failed too because of some missing libraries.

Any help is appreciated.
-H