Hi friend.
The standby control board does not support this command. The power-off operation applies only to the service board that communicates with the main control board, not the main control board and power interface board.

For details about how to use this command, click: board power-off
NOTE: After a board is powered off, the services on the board are interrupted. Therefore, to prevent the services from being interrupted, exercise caution when running this command.
Thanks.