This error typically appears on Oppo and Realme devices when you try to access the bootloader (Fastboot mode) after a failed unlock attempt or an unauthorized firmware change . It essentially means the device's security system is blocking the bootloader because the "unlock verification" process doesn't recognize your serial number as authorized . Why This Happens

can sometimes bypass serial verification to flash firmware or unlock the bootloader. Official Unlock App

In essence, the phone is rejecting the unlock command because the authorization key (or the expected serial number format) is incorrect or missing.

: Some users report this error specifically after updating to newer Android versions (like Android 11 or 13), where the system's internal verification becomes stricter. Known Fixes and Workarounds