How to fix AR build failed?

I have been following the video:
Installing & Building to Android (AR, VR, Mobile) UE4 / Unreal Engine 4 - YouTube
But then (In the log output) I got this, in the end:

Please, help. What did I do wrong?

I went back to Project Settings>Platform>Android SDK and adjusted SDK API and NDK API from “latest” to 21 and it failed.

So I went back to The AnswerHub and found this:

Followed the suggestion to "…disable “enable grade instead of ant” and disabled it and got this: