When using fwupdate with Oracle SPARC M series platforms, you can only update the main SP and must use the --remote-hostname and --remote-username options to in the command line. Attempts to run fwupdate against the local SP will result in an error and cancel the update.
Always refer to the specific README instructions included with firmware released for the Oracle SPARC M series platforms as this issue might not be applicable to all versions of M-series firmware.