How to add payload request for FB chatbot in python?

I have created a chatbot in python, flask, pymessenger, witai. I have added some button but I don't know how to reply back once the user press/select the option from my menu. Below is my code.

@app.route('/', methods=['GET'])
def verify():
    if request.args.get("hub.mode") == "subscribe" and request.args.get("hub.challenge"):
        if not request.args.get("hub.verify_token") == "hello":
            return "Verification token mismatch", 403
        return request.args["hub.challenge"], 200
    return "Hello World", 200

@app.route('/', methods=['POST'])
def webhook():
    data = request.get_json()
    log(data)

    if data['object'] == 'page':
        for entry in data['entry']:
            for messaging_event in entry['messaging']:

                sender_id = messaging_event['sender']['id']
                recipient_id = messaging_event['recipient']['id']

                if messaging_event.get('message'):
                    if 'text' in messaging_event['message']:
                        messaging_text = messaging_event['message']['text']
                    else:
                        messaging_text = 'no text'

                    response = None

                    entity, value = wit_response(messaging_text)

                    if entity == 'cust_id':
                        test = cust(str(value))
                        buttons = []
                        button = Button(title='1. Pizza', type='postback', payload='Pizza')
                        buttons.append(button)
                        button = Button(title='2. Burger', type='postback', payload='Burger')
                        buttons.append(button)
                        button = Button(title='3. Pasta', type='postback', payload='Pasta')
                        buttons.append(button)
                        text = 'Hey '+test[0] +'👋.'+"\n"+'Select Option:'
                        bot.send_button_message(sender_id, text, buttons)

I don't know after the user chooses one option how to handle the request. For example, if the user selects Pizza, I want to return the pizza menu in text or button format.

You can retrieve the payload from data

if 'postback' in data['entry'][0]['messaging'][0] :  
    payload = data['entry'][0]['messaging'][0]['postback']['payload']
    sender = data['entry'][0]['messaging'][0]['sender']['id']