The frequency of a donation level should be part of the API's response.  Since the frequency isn't currently specified in the API response it would be very easy to accidentally generate a donation that was meant to take single gifts that instead took monthly (or vice versa). It would destroy a charity's reputation if they used your API to generate a form to collect single donations but instead it started charging constituents monthly. Also, it would be very damaging to a charity's bottom line if instead of creating a recurring donation it only collected a one time donation.