如何正确地将数据从Android App发布到PHP？

I'm developing an app that has to post user data to database (login,password,id of device, latitude and longitude). I'm trying to POST it through PHP, but i get eror "End of input at line 1 column 1 path $".

I'm not sure what should I do.

I was trying to do something with gson, but it didn't work also. If anyone has any idea, please let me know... :)

Here is my MainActivity Code:

public void createPost(String loginStr, String passwordStr, String id_urzadzenia, double latitude, double longitude) throws IOException {
    Gson gson = new GsonBuilder()
            .setLenient()
            .create();

    Retrofit retrofit = new Retrofit.Builder()
            .baseUrl("https://unpreached-courtesy.000webhostapp.com")
            .addConverterFactory(GsonConverterFactory.create(gson))
            .build();
    API ApiPlaceHolder = retrofit.create(API.class);

    Call<Post> call = ApiPlaceHolder
            .createPost(
                    loginStr,
                    passwordStr,
                    id_urzadzenia,
                    latitude,
                    longitude);

    call.enqueue(new Callback<Post>() {
        @Override
        public void onResponse(Call<Post> call, Response<Post> response) {
            if (!response.isSuccessful()) {
                Toast.makeText(MainActivity.this, "Code " + response.code(), Toast.LENGTH_SHORT).show();

            }

        }

        @Override
        public void onFailure(Call<Post> call, Throwable t) {
            Toast.makeText(MainActivity.this, t.getMessage(), Toast.LENGTH_LONG).show();
            Toast.makeText(MainActivity.this, call.request().toString(), Toast.LENGTH_SHORT).show();
        }
    });

}

API Interface code:

public interface API {
    @FormUrlEncoded
    @POST("/dane.php")
        Call<Post> createPost (
                @Field("loginStr")String loginStr,
                @Field("passwordStr") String passwordStr,
                @Field("id_urzadzenia") String id_urzadzenia,
                @Field("latitude") double latitude,
                @Field("longitude") double longitude
                );
}

Post.java class code:

public class Post {
    private String loginStr;

    private String passwordStr;

    private String id_urzadzenia;

    private double latitude;
    private double longitude;

    public String getLoginStr() {
        return loginStr;
    }

    public void setLoginStr(String loginStr) {
        this.loginStr = loginStr;
    }

    public String getPasswordStr() {
        return passwordStr;
    }

    public void setPasswordStr(String passwordStr) {
        this.passwordStr = passwordStr;
    }

    public String getId_urzadzenia() {
        return id_urzadzenia;
    }

    public void setId_urzadzenia(String id_urzadzenia) {
        this.id_urzadzenia = id_urzadzenia;
    }

    public double getLatitude() {
        return latitude;
    }

    public void setLatitude(double latitude) {
        this.latitude = latitude;
    }

    public double getLongitude() {
        return longitude;
    }

    public void setLongitude(double longitude) {
        this.longitude = longitude;
    }
}

And there is my PHP:

    <?php header('Content-Type: application/json');



$con = mysqli_connect(DB_SERVER,DB_USER,DB_PASSWORD,DB_DATABASE);


$login = $_POST["loginStr"];
$id_urz = $_POST["id_urzadzenia"];
$dl_geo = $_POST["longitude"];
$sz_geo = $_POST["latitude"];
echo "Login użytkownika: " .$login . "
";
echo "ID urządzenia: " . $id_urz . "
";
echo "Szerokość geograficzna: " . $sz_geo . "
";
echo "Długość geograficzna: " . $dl_geo . "
";
date_default_timezone_get(Europe);
$godz =  date("H:i:s");
$sql = "INSERT INTO TABLE bartek (id_urzadzenia,szerokosc,dlugosc,data) VALUES ('".json_encode($id_urz)."','".json_encode($sz_geo)."','".json_encode($dl_geo)."','".$godz."'";

mysqli_query($con, $sql);
mysqli_close($con);
?>