I followed all the steps of the tutorial but still libreactnativejni.so is not getting generated for arm64-v8a. It gets generated only for armeabi-v7a. This is the stack trace for reference.

2019-09-11 03:46:06.633 24372-26863/design.zeta.spaced E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #1
    Process: design.zeta.spaced, PID: 24372
    java.lang.RuntimeException: An error occurred while executing doInBackground()
        at android.os.AsyncTask$3.done(AsyncTask.java:353)
        at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:383)
        at java.util.concurrent.FutureTask.setException(FutureTask.java:252)
        at java.util.concurrent.FutureTask.run(FutureTask.java:271)
        at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:245)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1162)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:636)
        at java.lang.Thread.run(Thread.java:764)
     Caused by: java.lang.UnsatisfiedLinkError: could find DSO to load: libreactnativejni.so
        at com.facebook.soloader.SoLoader.loadLibraryBySoName(SoLoader.java:213)
        at com.facebook.soloader.SoLoader.loadLibrary(SoLoader.java:178)
        at com.facebook.react.bridge.JSCJavaScriptExecutor.<clinit>(JSCJavaScriptExecutor.java:25)
        at com.facebook.react.bridge.JSCJavaScriptExecutor$Factory.create(JSCJavaScriptExecutor.java:20)
        at com.facebook.react.ReactInstanceManagerImpl$ReactContextInitAsyncTask.doInBackground(ReactInstanceManagerImpl.java:183)
        at com.facebook.react.ReactInstanceManagerImpl$ReactContextInitAsyncTask.doInBackground(ReactInstanceManagerImpl.java:169)
        at android.os.AsyncTask$2.call(AsyncTask.java:333)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:245) 
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1162) 
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:636) 
        at java.lang.Thread.run(Thread.java:764)