dreamhouse-bot-messenger wrong validation token error

I am currently following a tutorial to config a Salesforce bot that works with Facebook messenger.

This is the tutorial: https://github.com/dreamhouseapp/dreamhouse-bot-messenger

I followed all the steps but the bot doesn't answer on questions like "Find houses in Boston". I also find out that I have an error on my app page on Heroku. If I go to https://.herokuapp.com/webhook I returns the following error: Error, wrong validation token.

Can anyone help with this?

Thanks in advance

via HazHaz