When I toggle on the install via USB in developer mode:
I had the exact same problem, tried all the suggested workarounds, but none of them worked for me. Strangely enough, what actually has worked for me was turning on MIUI optimization (it was turned off when the problem occurred)! After turning it on, I was able to toggle on install via USB.
If turning your Wi-Fi off is not working for you, then you might have not yet registered your MIUI account as a developer account.
To do so go to MIUI Dev center and register your already created account. After the review process this should not be bugging you anymore.
But remember as other have noted to:
In my case,
I turned on Airplane mode
and
turn it off
then
turn off Wifi
and
turn on mobile data
.
Now I can turn on install via USB.
May it helps some one like me.
(1) Turn Off your Wi-Fi
(2) Turn On your Mobile Data
(3) Turn On "Install via USB" from Developer Option of your device.
That's all
Please verify your email and phone number in Mi account first then try this:
Try this