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I am trying to receive OTP number from Firebase using Android App. I am getting OTP every time after phone restarts and after that I am not getting any OTP. Any help is highly appreciated. My project contains below four activities.

Options Tried to resolve this issue

1. Cleared the Data on the phone. Its same issue for other users too.

You should first remove

 FirebaseAuth.getInstance().signOut();
 FirebaseAuth.getInstance().signOut();
 FirebaseAuth.getInstance().signOut();
 FirebaseAuth.getInstance().signOut();
 FirebaseAuth.getInstance().signOut();

Shouldn't be called 5 times in a row. Just do it once and in onStop method:

override fun onStop() 
 super.onStop()
 FirebaseAuth.getInstance().signOut()

I think you should then set

FirebaseApp.initializeApp(this);

only once and be sure to put this preferably in your custom Application class:

class CustomApplication : Application() 
override fun onCreate() 
 super.onCreate()

 /**
 * Firebase Initialization code
 * **/

 FirebaseApp.initializeApp(this)

Then, in your Manifest.xml file:

<application
 android:name=".CustomApplication"
 android:allowBackup="true"
 android:fullBackupContent="true"
 android:icon="@mipmap/ic_launcher"
 android:label="@string/app_name"
 android:largeHeap="true"
 android:supportsRtl="true"
 android:theme="@style/AppTheme">

....
....

</application>

Official Firebase github Repo

In addition, be sure to check out the example code for Firebase/quickstart-android - PhoneAuthActivity for phone authentication of the official repository:
quickstart-android for phone authentication

You should then be ready to go with proper phone authentication implementation with Firebase.