How to get messages from telegram bot with webhook?

Question

Python

Good afternoon!

I am transferring bots to webhook, to test the webhook, I took an example from the pytelegramBotAPI module using flask. I receive messages from telegrams on a webhook, but I can’t process them, namely, if I use the function from the example:

@app.route(WEBHOOK_URL_PATH, methods=['POST'])
def webhook():
    if flask.request.headers.get('content-type') == 'application/json':
        json_string = flask.request.get_data().decode('utf-8')
        update = telebot.types.Update.de_json(json_string)
        bot.process_new_updates([update])
        return ''
    else:
        flask.abort(403)

# Handle '/start' and '/help'
@bot.message_handler(commands=['help', 'start'])
def send_welcome(message):
    bot.reply_to(message,
                 ("Hi there, I am EchoBot.\n"
                  "I am here to echo your kind words back to you."))

Then after starting and sending a message to the bot, nothing happens.
But if I change the function :

@app.route(WEBHOOK_URL_PATH, methods=['POST'])
def webhook():
    update = flask.request.get_json()
    print(update)
    if 'message' in update:
        text = update['message']['text']
        chat_id = update['message']['chat']['id']
        bot.send_message(chat_id, 'you said "{}"'.format(text))
    return "ok", 200

After sending a message to the bot, I get it as an output and a response in telegram. Can you please tell me why the example from the module itself does not work?