SinchClient used for voip integration

Question

I am using the SinchClient for Voip integration in my audio device. I have Created the VOIPClient.Java is like below.

public class VOIPClient {
private static final String TAG = "VOIPClient";

private SinchClient mSinch = null;
private TTSHelper mTTS;
private Call mCurrentCall;
private BootService mContext;
private NsdController mNsdController;

private final CallListener mCallListener = new CallListener() {
    @Override
    public void onCallProgressing(Call call) {
        Log.d(TAG, "Call established at " + " Thusee");
    }

    @Override
    public void onCallEstablished(Call call) {
        Log.d(TAG, "Call established at " + call.getDetails().getEstablishedTime());
        mTTS.speak("Call started", TTSHelper.UTTERANCE_VOIP_START);

        JsonObject payload = new JsonObject();
        payload.addProperty("Status", 0);
        payload.addProperty("Call_status", 1);

        if (mNsdController != null) {
            mNsdController.sendCommand(20, payload);
        }

    }

    @Override
    public void onCallEnded(Call call) {
        Log.d(TAG, "Call ended at " + call.getDetails().getEndedTime() + "caused by " + call.getDetails().getEndCause().toString());

        //TODO : null object reference hangup
        if (mCurrentCall != null) {
               mTTS.speak("Call ended", TTSHelper.UTTERANCE_VOIP_END);
            mCurrentCall.hangup();

            return;
        }
        // mContext.getAlexa().start();

        JsonObject payload = new JsonObject();
        payload.addProperty("Status", 0);
        payload.addProperty("Call_status", 1);

        if (mNsdController != null) {
            mNsdController.sendCommand(21, payload);
        }
    }

    @Override
    public void onShouldSendPushNotification(Call call, List<PushPair> list) {

    }
};

public VOIPClient(BootService context) {
    mContext = context;
    mTTS = TTSHelper.getInstance(context);

    if (mNsdController != null)
        mNsdController.initialize();
}

public void start() {
    SharedPreferences prefs = mContext.getPreferences();
    int userId = prefs.getInt(MerryClient.PREF_USER_ID, 0);
    String mUserId;

        if (mSinch == null) {
            mUserId = String.valueOf(userId);
            mSinch = Sinch.getSinchClientBuilder().context(mContext.getApplicationContext()).userId(mUserId)
                    .applicationKey(CloudConfig.SINCH_APP_KEY)
                    .applicationSecret(CloudConfig.SINCH_APP_SECRET)
                    .environmentHost(CloudConfig.SINCH_ENVIRONMENT).build();

            mSinch.setSupportCalling(true);
            mSinch.setSupportManagedPush(false);

            mSinch.addSinchClientListener(new MySinchClientListener());

            mSinch.getCallClient().setRespectNativeCalls(false);
            mSinch.getCallClient().addCallClientListener(new SinchCallClientListener());

            mCurrentCall = null;

            mSinch.startListeningOnActiveConnection();
            mSinch.start();
    }
}

public void tearDown() {
    if (mSinch != null) {
        mSinch.stopListeningOnActiveConnection();
        mSinch.terminate();
        mSinch = null;
    }
}

public void restart() {
    tearDown();
    start();
}

public void initiateCall(final String targetUserName) {

    Handler mainHandler = new Handler(mContext.getMainLooper());
    mainHandler.post(new Runnable() {
        @Override
        public void run() {
            if (targetUserName != null) {
                try {
                    Call call = callUser(targetUserName);
                    call.addCallListener(mCallListener);
                    mCurrentCall = call;

                } catch (Exception e) {
                    Log.e(TAG, "Initiate VOIP call failed", e);
                    // mContext.getAlexa().start();
                }
            }
        }
    });
}


public void answerCall() {
    if (mCurrentCall != null) {
        //   mContext.getAlexa().tearDown();
        mCurrentCall.answer();
    }
}

public void hangUpCall() {
    if (mCurrentCall != null) {
        mCurrentCall.hangup();
    }
}

private class SinchCallClientListener implements CallClientListener {
    @Override
    public void onIncomingCall(CallClient callClient, Call call) {
        //  mContext.getAlexa().stop();
        Log.d(TAG, "Incoming call");
        mTTS.speak("Incoming call from " + call.getRemoteUserId(), TTSHelper.UTTERANCE_VOIP_INCOMING);
        call.addCallListener(mCallListener);
        mCurrentCall = call;

        // For testing only
        answerCall();
    }
}

public Call callUser(String userId) {
    if (mSinch == null) {
        start();
    }

    return mSinch.getCallClient().callUser(userId);
}


private class MySinchClientListener implements SinchClientListener {

    @Override
    public void onClientStarted(SinchClient sinchClient) {
        Log.d(TAG, "Sinch Client starts: " + sinchClient.getLocalUserId());
        mTTS.speak("Call ready", TTSHelper.UTTERANCE_VOIP_READY);
    }

    @Override
    public void onClientStopped(SinchClient sinchClient) {
        Log.d(TAG, "SinchClient stopped");
    }

    @Override
    public void onClientFailed(SinchClient sinchClient, SinchError sinchError) {
        Log.e(TAG, String.format("Sinch Client error %d: %s", sinchError.getCode(), sinchError.getMessage()));
                    mSinch.stopListeningOnActiveConnection();
        mSinch.terminate();
        mTTS.speak("Voice Over IP failed", TTSHelper.UTTERANCE_VOIP_FAIL);
    }

    @Override
    public void onRegistrationCredentialsRequired(SinchClient sinchClient, ClientRegistration clientRegistration) {
        Log.d(TAG, "Sinch Client requires registration");
    }

    @Override
    public void onLogMessage(int i, String s, String s1) {
        Log.d(TAG, s1);
    }
}

}

I have initialized this instance in the service, calling

VOIPClient mVoip = new VOIPClient(this);

then I start the SinchClient from the NSD command class like this

 Handler mainHandler = new Handler(mBootService.getMainLooper());
    mainHandler.post(new Runnable() {
        @Override
        public void run() {
            LocalRepository.getInstance().saveMerrySetupString("MerrySetup");

            mBootService.getVOIP().start();

        }
    });

then it starts the sinchClient. again If I tried to call to other device it's calling the method like this `

public void initiateCall(final String targetUserName) {

    Handler mainHandler = new Handler(mContext.getMainLooper());
    mainHandler.post(new Runnable() {
        @Override
        public void run() {
            if (targetUserName != null) {
                try {
                    Call call = callUser(targetUserName);
                    call.addCallListener(mCallListener);
                    mCurrentCall = call;

                } catch (Exception e) {
                    Log.e(TAG, "Initiate VOIP call failed", e);
                    // mContext.getAlexa().start();
                }
            }
        }
    });
}

then first time I can able to get the call then second time I am getting the exception like below

java.lang.IllegalStateException: SinchClient not started
at com.sinch.android.rtc.internal.client.calling.DefaultCallClient.throwUnlessStarted(Unknown Source)
at com.sinch.android.rtc.internal.client.calling.DefaultCallClient.call(Unknown Source)
at com.sinch.android.rtc.internal.client.calling.DefaultCallClient.callUser(Unknown Source)
at com.sinch.android.rtc.internal.client.calling.DefaultCallClient.callUser(Unknown Source)
at tw.com.test.cloud.VOIPClient.callUser(VOIPClient.java:272)
at tw.com.test.cloud.VOIPClient$CallerThread.run(VOIPClient.java:293)
at java.lang.Thread.run(Thread.java:818)

Anyone suggest the solution for this? its getting

Is it threading issue? Please suggest the solution for this I can't make the call hereafter