Function Calling with API Assistant playground

Greetings, i would like to use functions within the playground to query some data to use them for answers. (Like the actions for custom gpts)

For this i have build a test JSON output and created the function

{
  "name": "fetchModelData",
  "description": "Fetch model data from a given URL",
  "parameters": {
    "type": "object",
    "properties": {
      "api_url": {
        "type": "string",
        "description": "The URL to fetch the model data from",
        "default": "https://bot.gsdfsfrk.eu/apitest/"
      }
    },
    "required": [
      "api_url"
    ]
  }
}

The result of this that he starts the function and i get only a button that i have to submit some query

What can i do to get this fixed? Is it not possible to use functions within the playground assistant without further coding of as example a python script?