Post запрос в json используя retrofit2

Помогите с POST запросом retrofit. Ни как не даётся для изучения! При использование примера ниже и нажатии на кнопку в приложение выдаёт ошибку:

E/MainActivity: onResponse: null

Добавил ещё один класс ApiClients в нём указал данные для отправки. Объявил его в MainActivity все равно ту же ошибку выдаёт

Вся документация с работающим API https://faucetpay.io/page/api-documentation

В приложение есть button, при нажатии на которую нужно сделать POST запрос с отправкой в JSON: ключа, суммы, кошелька, и валюты.

Адрес для отправки: https://faucetpay.io/api/v1/send

Пример данных для отправки:

КЛЮЧ: api_key=74445766369c0ebe19ca067471be1b41be398f5c
СУМА: amount=50
КОШЕЛЁК: to=MQYSDrNwiJxr1VmLiJHNqaMtJeNon5NUGn
ВАЛЮТА: currency=LTC

Пример ответа на запрос

{
    "status": 200,
    "message": "OK",
    "rate_limit_remaining": 9.99780024,
    "currency": "BTC",
    "balance": "8673047351",
    "balance_bitcoin": "86.73047351",
    "payout_id": 109,
    "payout_user_hash": "c448e31098a8dfb48248f7e2374e77674bb90925"
}

Мой activity

    <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="GET TODOS"
        android:onClick="getTodos"/>

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="POST TODOS"
        android:onClick="postTodos"/>

</LinearLayout>

Мой MainActivity class

        public class MainActivity extends AppCompatActivity {


    private static final String TAG = "MainActivity";
    ApiInterface apiInterface;

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

        apiInterface = ApiClient.getClient().create(ApiInterface.class);

    }

    public void getTodos(View view) {

        Call<List<Todo>> call = apiInterface.getTodos();
        call.enqueue(new Callback<List<Todo>>() {
            @Override
            public void onResponse(Call<List<Todo>> call, Response<List<Todo>> response) {
                Log.e(TAG, "onResponse: " + response.body());
            }

            @Override
            public void onFailure(Call<List<Todo>> call, Throwable t) {
                Log.e(TAG, "onFailure: " + t.getLocalizedMessage());
            }
        });

    }

    public void postTodos(View view) {

        ApiClients apiClients = new ApiClients("74413496369c0eb1e9ca067421bccb41be398f5c", 50, "MQYSDrNwiJxr1VmLiJHNqaMtJeNon5NUGn", "LTC");
        Call<ApiClients> apiClientsPostCall = apiInterface.postApiClients(apiClients);
        apiClientsPostCall.enqueue(new Callback<ApiClients>() {
            @Override
            public void onResponse(Call<ApiClients> call, Response<ApiClients> response) {
                Log.e(TAG, "onResponse: " + response.body());
            }

            @Override
            public void onFailure(Call<ApiClients> call, Throwable t) {

            }
        });

    }


}

Мой ApiClient class

public class ApiClient {

    private static final String BASE_URL = "https://faucetpay.io/api/v1/";
    private static Retrofit retrofit = null;

    public static Retrofit getClient(){
        if(retrofit == null){
            retrofit = new Retrofit.Builder()
                    .baseUrl(BASE_URL)
                    .addConverterFactory(GsonConverterFactory.create())
                    .build();
        }

        return retrofit;
    }
}

Мой ApiInterface interface

public interface ApiInterface {

    @GET("/send")
    Call<List<Todo>> getTodos();

    @POST("/send")
    Call<ApiClients> postApiClients(@Body ApiClients apiClients);
}

Мой Todo class

public class Todo {

private int status;
private String message;
private double rate_limit_remaining;
private String currency;
private double balance;
private double balance_bitcoin;
private int payout_id;
private String payout_user_hash;

public Todo(int status, String message, double rate_limit_remaining, String currency, double balance, double balance_bitcoin, int payout_id, String payout_user_hash) {
    this.status = status;
    this.message = message;
    this.rate_limit_remaining = rate_limit_remaining;
    this.currency = currency;
    this.balance = balance;
    this.balance_bitcoin = balance_bitcoin;
    this.payout_id = payout_id;
    this.payout_user_hash = payout_user_hash;
}

public int getStatus() {
    return status;
}

public void setStatus(int status) {
    this.status = status;
}

public String getMessage() {
    return message;
}

public void setMessage(String message) {
    this.message = message;
}

public double getRate_limit_remaining() {
    return rate_limit_remaining;
}

public void setRate_limit_remaining(double rate_limit_remaining) {
    this.rate_limit_remaining = rate_limit_remaining;
}

public String getCurrency() {
    return currency;
}

public void setCurrency(String currency) {
    this.currency = currency;
}

public double getBalance() {
    return balance;
}

public void setBalance(double balance) {
    this.balance = balance;
}

public double getBalance_bitcoin() {
    return balance_bitcoin;
}

public void setBalance_bitcoin(double balance_bitcoin) {
    this.balance_bitcoin = balance_bitcoin;
}

public int getPayout_id() {
    return payout_id;
}

public void setPayout_id(int payout_id) {
    this.payout_id = payout_id;
}

public String getPayout_user_hash() {
    return payout_user_hash;
}

public void setPayout_user_hash(String payout_user_hash) {
    this.payout_user_hash = payout_user_hash;
}


@Override
public String toString() {
    return "Todo{" +
            "status=" + status +
            ", message='" + message + '\'' +
            ", rate_limit_remaining=" + rate_limit_remaining +
            ", currency='" + currency + '\'' +
            ", balance=" + balance +
            ", balance_bitcoin=" + balance_bitcoin +
            ", payout_id=" + payout_id +
            ", payout_user_hash='" + payout_user_hash + '\'' +
            '}';
}
}

Мой новый ApiClients class для отправки данных

public class ApiClients {

    private String api_key;
    private int amount;
    private String to;
    private String currency;

    public ApiClients(String api_key, int amount, String to, String currency) {
        this.api_key = api_key;
        this.amount = amount;
        this.to = to;
        this.currency = currency;
    }

    public String getApi_key() {
        return api_key;
    }

    public void setApi_key(String api_key) {
        this.api_key = api_key;
    }

    public int getAmount() {
        return amount;
    }

    public void setAmount(int amount) {
        this.amount = amount;
    }

    public String getTo() {
        return to;
    }

    public void setTo(String to) {
        this.to = to;
    }

    public String getCurrency() {
        return currency;
    }

    public void setCurrency(String currency) {
        this.currency = currency;
    }

    @Override
    public String toString() {
        return "ApiClients{" +
                "api_key='" + api_key + '\'' +
                ", amount=" + amount +
                ", to='" + to + '\'' +
                ", currency='" + currency + '\'' +
                '}';
    }
}

Данное приложение делал по примеру видео с ютуба