How to Unlock Bootloader Masstel M421 with Fastboot Method.
The Bootloader is a code that always runs when someone power on its device. Some hardware starts automatically and gets the boot process then loads the kernel and ramdisk. That is the Bootloader. It allows you to Root your Masstel M421, Flash TWRP, and Custom ROM in a simple easy method.
You can install any custom ROM like Lineage OS, Resurrection ROM, etc.
On this page, you will learn how to unlock the bootloader on your Masstel M421. Using the bootloader you can install custom ROM, custom recovery, custom kernel, and flash the factory images, etc. The bootloader will help you to unlock your device legally binding, but it will affect the device warranty. Masstel doesn’t allow you to unlock the bootloader. Mostly Android OEM manufacturers lock the bootloader, if you want to install any CUSTOM ROM, you must need to unlock the bootloader of your M421. It will void the warranty.
Firstly, you need to enable the Developer Options on your Masstel M421.
Go to Settings->>About Phone->> and press the Build Number 6 to 7 times until you see a pop message that shows you “You are now a developer”.
Into the Developer Options, now you need to Enable USB Debugging, and the OEM Unlock Option.
After that, again head to the Settings>>>>Developer Options>>>>enable USB Debugging and OEM Unlock.
Download and setup the ADB and Fastboot tools on your Computer.
Now, connect your M421 to your Laptop/PC using a USB cable.
Now, you should wait until all the USB drivers installed on your computer.
Now open the CMD or command prompt and go to the same folder, where you have extracted the contents of the ADB and Fastboot tools.
After that, type the below command into the command prompt area and press the Enter button;
You will see a popup message on your smartphone such as “Always allow from this computer”. Now You can press the OK button.
You should type the below command to enter the bootloader mode, and press Enter; button on your keyboard.
Now, type this commonds: "ADB reboot bootloader"
Now, you must enter the below command so your M421 and you will reboot into Fastboot mode;
Also, type this commond: "Fastboot flashing unlock"
Now, enter again your device into the Fastboot mode using the Volume Down + Power button together.
After that, enter the this command; "Fastboot flashing unlock_critical"
That’s It! You have successfully unlocked the bootloader of the Masstel M421 device.
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The Bootloader unlocking process will affect your Masstel M421 phone data like images, videos, and files. We advise you before start unlocking bootloader you need to create a backup and save it in a safe location.