code: func (api *API) AvailableZoneRatePlans(zoneID string) ([]ZoneRatePlan, error) {
  	uri := "/zones/" + zoneID + "/available_rate_plans"
  	res, err := api.makeRequest("GET", uri, nil)
  	if err != nil {
  		return []ZoneRatePlan{}, errors.Wrap(err, errMakeRequestError)
  	}
  	var r AvailableZoneRatePlansResponse
  	err = json.Unmarshal(res, &r)
  	if err != nil {
  		return []ZoneRatePlan{}, errors.Wrap(err, errUnmarshalError)
  	}
  	return r.Result, nil
  }
docs: // AvailableZoneRatePlans returns information about all plans available to the specified zone.
  //
  // API reference: https://api.cloudflare.com/#zone-plan-available-plans