Solution to "fastboot unlock verify fail" issue on OPPO#
Today, my 5-year-old OPPO suddenly pushed a system update to me. Excitedly, I directly clicked on the update without realizing that I had already rooted my phone. As a result, I lost root access after entering the system.
After resetting the system settings and entering developer mode, I found that the OEM unlock option was grayed out and the status was "Bootloader Unlocked". This made me worried. Unexpectedly, I encountered another surprise - I couldn't enter fastboot mode.
Image borrowed from a user on the xda forum
Serial is not match
fastboot unlock verify fail
The literal meaning is simple: serial number error, fastboot unlock failed. Google searches revealed that this error occurs more frequently on OPPO, OnePlus, and Realme devices that use MediaTek chipsets. It seems to be the work of the same development team. Considering that I used mtkclient for unlocking, I immediately tried it out. However, I encountered a connection error. The exploration process was quite difficult. I tried almost all the methods that should have worked, spending 5 hours troubleshooting. Let me directly state the conclusion.
Solution#
This error occurs due to mtkclient forcefully unlocking the bootloader (BL), which causes a mismatch in the OEM code. Previously, mtkclient successfully patched this issue on older systems. The patching method (not the same one) can be seen in lkpatcher. However, the problem is that this patching method requires flashing the patched fastboot partition. Considering that the OEM unlock option is already unlocked, I had a sudden idea that mtkclient might be able to bypass this issue and perform the repair. Could there be other interfering factors? It was not until I was browsing the internet that I discovered that the OPPO account can lock the device. I immediately tried logging out of the OPPO account and tried mtkclient again. The result was a successful connection and boot repair. My root access was restored!
Conclusion#
It is best to perform flashing during noon because something is bound to go wrong in the morning or evening. This time, I learned my lesson.