FiiO M11 Plus Portable High-Resolution Lossless Wireless Music Player - Manual (Page 97)

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3) After tapping the firmware file, any operation is not permitted. Wait for a while
and then the M11 Plus will start to upgrade automatically.
4) Upon completion of the firmware upgrade, the M11 Plus will restart itself
automatically. After restarting, it can be used as usual.
Notes:
1) Please ensure the battery power is sufficient before upgrading (at least up to
30%);
2) If it fails, please check if the correct upgrade firmware is used;