Creating a login application

I'm trying to create the action post for a login application. OnClick submitBtn the application is closed. Regardless of the backend configuration, I did not expect this behavior. Can you please help me? Thanks in advance.

public class MainActivity extends AppCompatActivity {
    private TextView mResponseTv;
    private APIService mAPIService;
    private Button submitBtn;
    private EditText titleEt;
    private EditText bodyEt;

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

    Log.e("carrapato", "Unable to submit post to API.");

    final EditText titleEt = (EditText) findViewById(R.id.editText);
    final EditText bodyEt = (EditText) findViewById(R.id.editText2);
    Button submitBtn = (Button) findViewById(R.id.button);
    mResponseTv = (TextView) findViewById(R.id.tv_response);

    mAPIService = ApiUtils.getAPIService();

    submitBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Log.v("capiabas", "Unable 234234234 to API.");
            String title = titleEt.getText().toString().trim();
            String body = bodyEt.getText().toString().trim();
            if (!TextUtils.isEmpty(title) && !TextUtils.isEmpty(body)) {

                Log.v("clips", "Urerertert to API.");
                sendPost(title, body);


            }
        }


        public void sendPost(String title, String body) {

            Log.d("catapora", "Unable to submit post to API.");
            mAPIService.savePost(title, body, 1).enqueue(new Callback<Post>() {


              private static final String TAG = "MainActivity2" ;

                @Override
                public void onResponse(Call<Post> call, Response<Post> response) {



                    if (response.isSuccessful()) {
                        showResponse(response.body().toString());

                        Log.v("caixinha", "post submitted to API." + response.body().toString());
                    }
                }

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

        public void showResponse(String response) {
            if (mResponseTv.getVisibility() == View.GONE) {
                mResponseTv.setVisibility(View.VISIBLE);
            }
            mResponseTv.setText(response);
        }

    });
}
}

/

////////////////////////


public class ApiUtils {

private ApiUtils() {}

public static final String BASE_URL = "http://192.168.xxx";

public static APIService getAPIService() {

    Log.e("carrapato", "bbbb999999.");

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

/

      ////////////////////////////


 public interface APIService {


@POST("")
@FormUrlEncoded
Call<Post> savePost(@Field("title") String title,
                    @Field("body") String body,
                    @Field("userId") long userId);


 }

/

               /////////////////
 public class Post {

@SerializedName("title")
@Expose
private String title;
@SerializedName("body")
@Expose
private String body;
@SerializedName("userId")
@Expose
private Integer userId;
@SerializedName("id")
@Expose
private Integer id;

public String getTitle() {
    return title;
}

public void setTitle(String title) {
    this.title = title;
}

public String getBody() {
    return body;
}

public void setBody(String body) {
    this.body = body;
}

public Integer getUserId() {
    return userId;
}

public void setUserId(Integer userId) {
    this.userId = userId;
}

public Integer getId() {
    return id;
}

public void setId(Integer id) {
    this.id = id;
}

@Override
public String toString() {
    return "Post{" +
            "title='" + title + '\'' +
            ", body='" + body + '\'' +
            ", userId=" + userId +
            ", id=" + id +
            '}';
}

}