Open link in current tab with Rasa webchat

I am using Botfront’s webchat widget to integrate my chatbot in a website. I have a response with a button to open a url, which url is opened in a new browser tab by default. I would like to have it opened in the current tab.

From what I have seen, I can add metadata to my response to achieve what I want. However, I have problems making it work. Below you can see a snippet of the domain.yml generated by Botfront:

    - metadata:
        linkTarget: _self
        - title: Current tab
          type: web_url
          url: ''

When I try training the bot with that domain file (using Rasa open source, not Botfront), Rasa complains that the domain file is wrong, but it does not indicate where the problem is. I guess this is because the type and url fields are not recognized by Rasa for buttons.

I have also tried generating the response with metadata inside a custom action (this is actually what I want to do), but it did not work either. Hope someone can help me. Thanks!

@humcasma How about putting the metadata in the custom payload section of the response?