Hi, I’m new here.
My problem ? It’s impossible to import and synchronize my NC contacts on my Xiaomi contacts appli ! CardDav is well installed on my phone, my NC URL is well indicated in my Xiaomi contacts appli to synchronize my contacts, synchronization is well scheduled but no one synchronization is made !
Then synchronization of my contacts between NC and Thunderbird on my PC is OK.
Have you a solution ? Regards.
Please check your logfiles, are there errors? What does your contact app try to access (check the access log of your webserver)?
Hello! 
Have you tried using DavDroid? It’s basically doing the same but it works on my redmi 3.
Worth a try? 
I am using opensync for the synchronization. It works very well.
It is not the Yiaomi Redmi Note 4, but another android-phone.
As a side note and my opinion:
opensync is a fork of the DAVdroid project and I’d advise against using it:
DAVdroid is designed to be an open-source project (GPLv3) from the very first beginning. It is always possible to compile the app yourself and use it for free. The source code is available, and you can download the app on F-Droid.
However, it was and still is much work to create and maintain DAVdroid, so we have decided to put it in commercial stores for a small fee. If you want to support this project, please donate to DAVdroid or purchase it.
Rather please download the “original” app via f-droid or pay the small fee in the play store.
Tweet from DAVdroid on that topic: https://twitter.com/davdroidapp/status/881816279325302784