CRM function REST API response format

Is there a way to control the JSON response returned by the CRM function REST API?

If I call a function using either OAuth or an API key it returns a 200 OK response with a string in the format shown below.

I am using a particular feature of an external application (Slack) that doesn't allow me to strip out the JSON payload from the response so I'd like to be able to just send the JSON payload part on its own.

Is there a way to do this?

Grateful for any thoughts

Mark

{
    "code": "success",
    "details": {
        "output": "<<JSON payload>>",
        "output_type": "string",
        "id": "54509000003114113"
    },
    "message": "function executed successfully"
}