Hi there,
i just realized that inspecting your class you arent' checking the errors json encoded array from the response body of Mailchimp servers, if a 4xx error occourred, it should be interesting to have a getErrorsArray method on class to parse each error...
Do you think that will be possible?
Clearly, the last_error variable is populated with the status and detail of the formattedResponse, but that seems not to be enough for complete controlling the errors....

Thanks