POST request sending a String via Retrofit on Android

Question

I need a lot of help from you, I’m wanting to make a POST request via Retrofit, send only one parameter:

{
"select":"select id || ' | ' ||senha_terminal,nome,login_web,null,5,null n2,7,senha_terminal,senha_web,data_inclusao from usuario where id in (3257) order by id desc"
}

And in return I receive:

[
    {
        "campo1": "3257 | 74327",
        "campo2": "Sidnei",
        "campo3": "sidnei01",
        "campo4": null,
        "campo5": 5,
        "campo6": null,
        "campo7": 7,
        "campo8": "74327",
        "campo9": "56c07af798f309dbd75822a849ce47b6",
        "campo10": "2012-02-08T11:00:06"
    }
]

The method I use in Postman is the POST, using the url. I have done several tutorials of Retrofit, but none successfully. Someone could help?

My code: Apiutils:

public class ApiUtils {

    private ApiUtils() {}

    public static final String BASE_URL = "https://services-dev.redetendencia.com.br/api-rest/helper-qa/select/";

    public static APIService getAPIService() {

        return RetrofitClient.getClient(BASE_URL).create(APIService.class);
    }
}

Interface Apiservice:

import retrofit2.Call;
import retrofit2.http.Body;
import retrofit2.http.FormUrlEncoded;
import retrofit2.http.POST;

/**
 * Created by romeu on 27/03/18.
 */

public interface APIService {

    @POST("select")
    Call<Post> consulta(@Body JsonObject post);
}

Post:

package com.example.romeu.testedatabase;
import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

public class Post {

@SerializedName("campo1")
@Expose
private String campo1;
@SerializedName("campo2")
@Expose
private String campo2;
@SerializedName("campo3")
@Expose
private String campo3;
@SerializedName("campo4")
@Expose
private Object campo4;
@SerializedName("campo5")
@Expose
private Integer campo5;
@SerializedName("campo6")
@Expose
private Object campo6;
@SerializedName("campo7")
@Expose
private Integer campo7;
@SerializedName("campo8")
@Expose
private String campo8;
@SerializedName("campo9")
@Expose
private String campo9;
@SerializedName("campo10")
@Expose
private String campo10;

public String getCampo1() {
    return campo1;
}

public void setCampo1(String campo1) {
    this.campo1 = campo1;
}

public String getCampo2() {
    return campo2;
}

public void setCampo2(String campo2) {
    this.campo2 = campo2;
}

public String getCampo3() {
    return campo3;
}

public void setCampo3(String campo3) {
    this.campo3 = campo3;
}

public Object getCampo4() {
    return campo4;
}

public void setCampo4(Object campo4) {
    this.campo4 = campo4;
}

public Integer getCampo5() {
    return campo5;
}

public void setCampo5(Integer campo5) {
    this.campo5 = campo5;
}

public Object getCampo6() {
    return campo6;
}

public void setCampo6(Object campo6) {
    this.campo6 = campo6;
}

public Integer getCampo7() {
    return campo7;
}

public void setCampo7(Integer campo7) {
    this.campo7 = campo7;
}

public String getCampo8() {
    return campo8;
}

public void setCampo8(String campo8) {
    this.campo8 = campo8;
}

public String getCampo9() {
    return campo9;
}

public void setCampo9(String campo9) {
    this.campo9 = campo9;
}

public String getCampo10() {
    return campo10;
}

public void setCampo10(String campo10) {
    this.campo10 = campo10;
}

@Override
public String toString() {
    return "Post{" +
            "campo1='" + campo1 + '\'' +
            ", campo2='" + campo2 + '\'' +
            ", campo3='" + campo3 + '\'' +
            ", campo4=" + campo4 +
            ", campo5=" + campo5 +
            ", campo6=" + campo6 +
            ", campo7=" + campo7 +
            ", campo8='" + campo8 + '\'' +
            ", campo9='" + campo9 + '\'' +
            ", campo10='" + campo10 + '\'' +
            '}';
}

}

Retrofitclient:

public class RetrofitClient {

    private static Retrofit retrofit = null;

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

Mainactivity:

public class MainActivity extends AppCompatActivity {

    private APIService mAPIService;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mAPIService = ApiUtils.getAPIService();
        enviarConsulta("select id || ' | ' ||senha_terminal,nome,login_web,null,5,null n2,7,senha_terminal,senha_web,data_inclusao from usuario where id in (3257) order by id desc");
    }



    public void enviarConsulta(String query)
    {

        JsonObject data = new JsonObject(); data.addProperty("select", query);

        mAPIService.consulta(data).enqueue(new Callback<Post>() {
            @Override
            public void onResponse(Call<Post> call, Response<Post> response) {
                if(response.isSuccessful()) {
                    Log.d("SQL", "post submitted to API." + response.body().toString());
                }
            }

            @Override
            public void onFailure(Call<Post> call, Throwable t) {
                Log.d("SQL", "Unable to submit post to API.");
            }
        });
    }
}