How to handle different types of response in Fast Android Networking library

Question

I have success response and error response class. When error I get 200 status code. My question is to get the error json object to error kotlin class. How can I handle different types of response in FAN library. I have used JSONDeserializer in Java.

Success Response:

{
    "success": true,
    "terms": "https://currencylayer.com/terms",
    "privacy": "https://currencylayer.com/privacy",
    "timestamp": 1430401802,
    "source": "USD",
    "quotes": {
        "USDAED": 3.672982,
        "USDAFN": 57.8936,
        "USDALL": 126.1652,
        "USDAMD": 475.306,
        "USDANG": 1.78952,
        "USDAOA": 109.216875,
        "USDARS": 8.901966,
        "USDAUD": 1.269072,
        "USDAWG": 1.792375,
        "USDAZN": 1.04945,
        "USDBAM": 1.757305,
    [...]
    }
}

Error Response:

{
    "success": false,
    "error": {
        "code": 104,
        "info": "Your monthly usage limit has been reached. Please upgrade your subscription plan."    
  }
} 

My Code:

fun getCurrencies(): Disposable {
    return Rx2AndroidNetworking.get(GET_CURRENCY)
        .addQueryParameter(ACCESS_KEY, ACCESS_VALUE)
        .build()
        .getObjectObservable(Currency::class.java)
        .subscribeOn(Schedulers.io())
        .observeOn(AndroidSchedulers.mainThread())
        .subscribe({ currency ->
            run {
                if (currency.success) {
                    _currency.postValue(currency)
                }else {
                    // get error response
                    
                }
            }
        }, { err -> err.printStackTrace() })

}