How to fix Mi Account "Couldn't check device security info" and adding a phone number

 For fixing the "Couldn't check device security info" when we're trying to sign in to our Mi Account on the Xiaomi Account app is quite simple: download the latest Mi Account apk from Google, pick any trusted site like for example from apkmirror.

Install the latest app then try to sign in from the Mi Account in the Setting.

To add a phone number which is we won't be able to do that from our device since there's no such setting in the "Account Security" section.

Go to i.mi.com and sign in, you'll be shown with a page that looks like a Home screen with bunch of apps.

Select either "Recording" or "Contact" app there and you shall be prompted to add your phone number.

Add your phone number starting with the country code and followed by the phone number.

You'll be receiving a verification code via SMS, and done you have added your phone number.

You can then go to Mi Account from your phone Setting to confirm it.

I already had a phone number linked to my account earlier but it doesn't showed up on my account maybe because i don't insert the SIM card since it was already gone.

And thankfully i can add another new phone number to my old account with that trick.

I dont know what my old number is used for right now since it doesn't appears on my account.

Now you can do things that needed your Mi Account and phone number/SIM like "Install via USB", or "USB debugging" to simulate input.

Disclaimer that you have to insert your linked phone number SIM card on the first slot otherwise it won't work.

Source: https://www.reddit.com/r/LineageOS/comments/1d6y974/comment/lfhszom/