Native Portal requestBody content how to upload a file

[Wilown]

Hello everyone.
I looked a bit everywhere on the net but I couldn't find a definitive answer to my question.

I have a proxy that consume a csv file on a POST method.
the swagger bit for it is :

      requestBody:
        content:
            multipart/form-data:
              schema:
                type: object
                properties:
                    data:
                      type: string
                      format: binary

I can make it work on swagger editor, but I can't manage to do it on the native portal.
I have no visible way to load a file :


Is it even possible?
If yes, how ?
If no, is there a way to bypass it (maybe send only text, but I would like to refrain from modifying the proxy with java or javascript policies just to make the portal test pass).

I am sorry if this information is available somewhere else, but I couldn't find it.