XiaomiToolV2
Try this one: https://github.com/topminipie/XiaoMiToolV2
Or This: https://androidmtk.com/xiaomitool-v2
Solution
https://github.com/topminipie/awesome-xiaomi-bootloader-unlock#miunlocktool--mibypasstool--mitool
Download this: https://github.com/offici5l/MiUnlockTool
One device per Mi account per Month