I have just learned the hard way that newer models of mavic pros (with initial 1.3.1 FW or newer) cannot be simply downgraded, but must also be disassembled and an extra micro sd card must be inserted in order for the drone to work. Otherwise you will get "cannot take off message" and sd card error message.
It was also discussed on reddit: Suggestions please! Mavic pro is locked and cannot take off after mod • r/DJIUnlocked
It was also discussed on reddit: Suggestions please! Mavic pro is locked and cannot take off after mod • r/DJIUnlocked