code: func addHeaders(req *http.Request, headers map[string]interface{}) (bool, error) {
  	for k, v := range headers {
  		// Type assertion
  		header, ok := v.(string)
  		if ok {
  			req.Header.Add(k, header)
  		} else {
  			return false, fmt.Errorf("invalid type for headers value")
  		}
  	}
  	return true, nil
  }
docs: // Adds custom headers to a new HTTP request.