1. take about 3 days to 10 to recive the unlock permision
2. you can stop trying for 2 days, them try again, with a very good reason to do it, like if you need a app root for your study or work to funtion.
and they get a little faster to send you the unlock,
First Time I did it, took Xiaomi about 7 days
Second Time was like 4 days, but the second time, i did it again, and have a very specifc reason to do it,
3. do not expect to get the unlock the same day, you will only get mad.
SORRY FOR MY ENGLISH, I live in Honduras, Central America, spanish only, also I have Mi Max 32gb and the Mi Max 2 (the one I use )
Then need to login Mi account, enable Developer options, enable OEM unlock and press Add account and device button from dev options/Mi unlock status. Then boot to bootloader/fastboot mode and try to unlock again.
It should help if you make yourself more active in the MIUI.com forum by participating in discussions by posting your own mind. Once you have exposed yourself in several posts, it may be appropriate to seek permission to unlock the bootloader of your device. The permission is the most important because without it you cannot unlock the bootloader and subsequently root your device if you choose so.