code: protected final ResponseEntity<Response> setGreetingText(Payload[] greeting) {
          Event event = new Event().setGreeting(greeting);
          return restTemplate.postForEntity(fbMessengerProfileUrl, event, Response.class);
      }
docs: Call this method to set the "Greeting Text". A user sees this when it opens up the chat window for the
  first time. You can specify different messages for different locales. Therefore, this method receives an
  array of {@code greeting}.
  <p>
  See https://developers.facebook.com/docs/messenger-platform/discovery/welcome-screen for more.
  
  @param greeting an array of Payload consisting of text and locale
  @return response from facebook