code: public void unregister(final MFPPushResponseListener<String> listener) {
      MFPPushUrlBuilder builder = new MFPPushUrlBuilder(applicationId);
      if (this.deviceId == null) {
        this.deviceId = MFPPushUtils.getContentFromSharedPreferences(appContext, applicationId + DEVICE_ID);
      }
      String path = builder.getUnregisterUrl(deviceId);
      logger.debug("MFPPush:unregister() - The device unregister url is: " + path);
      MFPPushInvoker invoker = MFPPushInvoker.newInstance(appContext, path, Request.DELETE, clientSecret);
  
      invoker.setResponseListener(new ResponseListener() {
        @Override
        public void onSuccess(Response response) {
          logger.info("MFPPush:unregister() - Successfully unregistered device. Response is: " + response.toString());
          isTokenUpdatedOnServer = false;
          listener.onSuccess("Device Successfully unregistered from receiving push notifications.");
        }
  
        @Override
        public void onFailure(Response response, Throwable throwable, JSONObject jsonObject) {
  
          logger.error("MFPPush: Error while unregistered device");
          listener.onFailure(getException(response,throwable,jsonObject));
  
        }
      });
      invoker.execute();
    }
docs: Unregister the device from Push Server
  
  @param listener Mandatory listener class. When the subscription is deleted
  successfully the {@link MFPPushResponseListener}.onSuccess
  method is called with the tagName for which subscription is
  deleted. {@link MFPPushResponseListener}.onFailure method is
  called otherwise