The ID code is set in advance when the program in which the user set the ID code to addresses FFD4h to FFDAh is written to the flash memory. The ID in the M3A-0806 ID verification screen is used to verify the ID written to the flash memory. The ID the user inputs on this screen will not be written to the flash memory.
The first time the on-chip flash memory is programmed, ID verification will be successful no matter what value is input as the ID code in the ID verification screen (a value must be entered). If data has already been written to the flash memory, the value input in addresses FFD4h to FFDAh will become the ID code (including "FFh"). If you don't know the ID code, you can confirm it by looking up the value in addresses FFD4h to FFDAh in the HEX file of the program written to the on-chip flash memory. Note that if there are no existing values in addresses FFD4h to FFDAh of the HEX file, the ID code will be "FFh".
When ID match fails, reboot M3A-0806 and the MCU power supply.
Refer here for more on M3A-0806.