Unlocking bootloader for vivo devices Mediatek only!!
Tested Device 
y3/y12/y15/y17
y20 2021/y12s


• Download all the required files:
- Mediatek driver
- mtk-client 
- UsbDK
- Python latest is recommended

•Links

Mediatek Driver
https://www.mediafire.com/file/cjd3oewq8rujm8c/MTK_Driver_Setup.exe/file

UsbDk:
https://github.com/daynix/UsbDk/releases/

Mtk-Client:
https://github.com/bkerler/mtkclient/releases

Python:
https://www.python.org/downloads/


• Steps:
- Open Python that you have download and click add to PATH
- Install UsbDK
- Extract the mtk-client.zip to anywhere you want (desktop for more easier)
- Open command prompt and type this

cd (path-to-your-mtk-client-folder)
pip3 install -r requirements.txt
python mtk da seccfg unlock

- Prepare your phone, make sure it's turned off
- Connect your device into your pc with combined volume up and down
- Wait for it until succeeded 100%
- Unplug your device then turn it on
- You will see a message, ignore it
- If you stuck at logo, just wait for it, it will boot into recovery and requesting a factory reset.
- Factory reset it and congrats! You've unlock the bootloader for your vivo device.