def error_message
      response_body = JSON(response.body) rescue response.inspect
      {request_curl: as_curl, response_body: response_body}
    end
def error_message
      response_body = JSON(response.body) rescue response.inspect
      {request_curl: as_curl, response_body: response_body}
    end
Return the elements of the request/response that are worth displaying
 as an error message if the request fails.
 If the response format is JSON, showing the parsed body is sufficient,
 otherwise the whole (inspected) response is worth looking at.