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I was trying to unlock the bootloader of an old Redmi Note 4x, Downloaded fastboot and adb. I first enabled developer option and turned on USB debugging. I tried finding OEM unlock option which was not present on the phone. After few hours of searching about it online, I finally concluded it is not available for the phone. So I went on and fired up my terminal [in administrator mode];

$ adb devices
> List of devices attached
> 8H4DZP69S44DQOEM        device

then I rebooted my device in bootloader (fastboot)

$ adb reboot bootloader

My Phone restarted in bootloader, then I went back to my terminal and checked if the fastboot was working or not;

$ fastboot devices
> 8H4DZP69S44DQOEM        fastboot

After confirming that the fastboot is running, I tried unlocking OEM;

$ fastboot oem unlock
> (bootloader) Start unlock flow

> FAILED (remote: '
> Unlock failed - Err:0xffffffff
> ')
> fastboot: error: Command failed

which.. well... failed and I don't know why. I tried searching this very error code online but failed to find anything close to it.

My other attempts like unlocking flashing failed in similar fashion;

$ fastboot flashing unlock
> (bootloader) Start unlock flow

> FAILED (remote: '
> Unlock failed - Err:0xffffffff
> ')
> fastboot: error: Command failed

$ fastboot flashing unlock_critical
> (bootloader) Start unlock flow

> FAILED (remote: '
> Unlock failed - Err:0xffffffff
> ')
> fastboot: error: Command failed

Nothing seems to be working, Please help!

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    It doesn't work because you use a tutorial not meant to be used with your phone. Search for a matching tutorial and you will notice that you need the "MiFlashUnlock" tool en.miui.com/unlock/download_en.html
    – Robert
    Apr 2, 2022 at 13:35
  • I tried using MiFlashUnlock, when I try to sign in on my PC, it says that it needs to verify my phone number. And when I click on send CODE, the app prompts "Checking for security issues" and never stops loading. I still haven't got any OTP code, the tool is broken for me.
    – Thebluedragon
    Apr 3, 2022 at 10:59
  • you need mi account bonded to phone and sim activated for 7 days - RTFM ;)
    – alecxs
    Apr 3, 2022 at 12:42
  • The sim has been with me for almost a decade now, created an MI account during the unlocking. But it seems to get stuck while sending the OTP code with a prompt "Checking for security issue" which never ends.
    – Thebluedragon
    Apr 4, 2022 at 6:57
  • that's a broken CAPTCHA use QR-Code instead @Thebluedragon there exist instant unlock methods but requires some basic linux skills (@ me if interested)
    – alecxs
    Apr 4, 2022 at 18:37

1 Answer 1

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I solved mine when I enter in MI website and put my phone number and verified it on the website. After this, I tried again, and then something happens differently.

However, in the next step, you are going to have to unlock something in developer options. It required internet from a SIM card, not WiFi. After this, enable OEM unlock in the developer options to run the program, and then you have to wait for 200 hours.

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  • There's no "OEM unlock" option inside the developer option and I tried virtually everything I found on the internet.
    – Thebluedragon
    Aug 13, 2022 at 8:44

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