Install app via usb: The device is temporarily restricted

"Install via USB" wont work if your Xiaomi phone is running MIUI 8 or above. Looks like when you try to Enable this option, your phone trys to connect to some chinese server and fails.

I got a work around and it worked for me. Idea is to connect to Chinese-Shanghai server through VPN. Try the following:

1. Install PlexVPN from Playstore and login into it. You will get a 24 hr free VPN service.
2. Select China-Shanghai server and connect.
3. From developer option in your Xiaomi phone, Enable "Install via USB".
4. You can then disconnect the VPN and logout from PlexVPN.

Enjoy!!

All you have to do is Turn your Wi-Fi off, turn on mobile data, and then enable the setting for "Install via USB". It'll go through.

Source: http://en.miui.com/thread-544718-1-1.html

Turning off Wi-Fi and enabling Mobile Data (thank you Xiaomi for wasting my money to enabling mobile data which the last one I didn't have) on Xiaomi 4A did not work for me. Every time I tried to enable Install App Via USB it displayed me "the device is temporarily restricted". So, I found this solution:

Turn on VPN onto your device with these parameters and try again toggle Install from USB:

• Server Address: China server from https://www.vpngate.net/en/
• IPSec Key: vpn
• Username: vpn
• Password: vpn

For me on a rooted MIUI v.8.5.1 I just need to:

• turn off wifi
• turn on mobile connection In development options

after doing that both Install via USB and USB debugging started to work.