code: func PostJSON(ctx context.Context, rFn retry.Factory, c *http.Client, url string, headers map[string]string, in, out interface{}) (int, error) {
  	req, err := NewRequestJSON(ctx, c, rFn, url, "POST", headers, in, out)
  	if err != nil {
  		return 0, err
  	}
  	return req()
  }
docs: // PostJSON is a shorthand. It returns the HTTP status code and error if any.