Не работает YobitApi

Пытаюсь реализовать метод getInfo в API криптобиржи https://yobit.net/ru/api/

Приходит результат

{"success":0,"error":"invalid key, sign, method or nonce"}

Апи работает, есть примеры Python. На джаве примеров не густо(

Бьюсь уже несколько месяцев. В чём ошибка? код прикладываю:

Main activity

public class MainActivity extends AppCompatActivity {

public static final String SHARED_PREFS = "sharedPrefs";

public static SharedPreferences sharedPreferences;
public static SharedPreferences.Editor editor;

public static  String publicApi = "https://yobit.net/api/3/";
public static String tradeApi = "https://yobit.net/";
private static final String HMAC_SHA512 = "HmacSHA512";

public static  final String key = "";
public static  final String secret = "";

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    sharedPreferences = getSharedPreferences(SHARED_PREFS, MODE_PRIVATE);
    editor = sharedPreferences.edit();

        int nonce = sharedPreferences.getInt("nonce", 1);
        editor.putInt("nonce", ++nonce);
        editor.apply();

    String params = "method=getInfo&" + "nonce=" + nonce  ;

    HttpLoggingInterceptor httpLoggingInterceptor = new HttpLoggingInterceptor();
    httpLoggingInterceptor.setLevel(HttpLoggingInterceptor.Level.BODY);

    OkHttpClient.Builder okHttpClient = new OkHttpClient.Builder();
    okHttpClient.addInterceptor(httpLoggingInterceptor);

    OkHttpClient client = okHttpClient.build();

    Retrofit retrofit = new Retrofit.Builder()

            .baseUrl(tradeApi)
            .addConverterFactory(GsonConverterFactory.create())
            .addCallAdapterFactory(RxJavaCallAdapterFactory.create())
            .client(client)
            .build();

    try {

        String signParams = "";

        try {

            signParams = calculateHMAC(params, secret);

            String finalSign = signParams;
            okHttpClient.addInterceptor(chain -> {
                Request request = chain.request().newBuilder()

                        .addHeader("Key", key)
                        .addHeader("Sign", finalSign)

                        .build();

                return chain.proceed(request);
            });

            Api api = retrofit.create(Api.class);

            Call<ResponseBody> call = api.getInfo();

            call.enqueue(new Callback<ResponseBody>() {
                @Override
                public void onResponse(Call<ResponseBody> call, Response<ResponseBody> response) {
                    try {
                        Log.e("onResponse", response.body().string());
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }

                @Override
                public void onFailure(Call<ResponseBody> call, Throwable t) {
                    Log.e("onFailure", String.valueOf(t.getMessage()));
                }
            });


        } catch (SignatureException e) {
            e.printStackTrace();
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        } catch (InvalidKeyException e) {
            e.printStackTrace();
        }
    } finally {

    }
}

private static String toHexString(byte[] bytes) {
    Formatter formatter = new Formatter();
    for (byte b : bytes) {
        formatter.format("%02x", b);
    }
    return formatter.toString();
}

public static String calculateHMAC(String data, String key)
        throws SignatureException, NoSuchAlgorithmException, InvalidKeyException
{
    SecretKeySpec secretKeySpec = new SecretKeySpec(key.getBytes(), HMAC_SHA512);
    Mac mac = Mac.getInstance(HMAC_SHA512);
    mac.init(secretKeySpec);
    return toHexString(mac.doFinal(data.getBytes()));
}

}

Api

public interface Api {

    @POST("info")
    Call<Info> info();

    @POST("tapi/")
    Call<ResponseBody> getInfo();

}