How can I connect the rest api I wrote to my flutter project?

When I test my php files with postman, it works but I can’t run it with retrofit.

I am trying to write an API for the first time and both methods return an error on the resource status.

get: https://www.codeocean.net/codeocean/getdata.php
post: https://www.codeocean.net/codeocean/adddata.php (in the request body:

{
    "userName": "uzaktan ",
    "userSurname": "uzaktan ",
    "userBalance": 111,
    "userEmail": "uzaktan ",
    "userPassword": "123123"
}

)

mixinuserfeature.dart

  Future<Resource<List<UserModel>>> getData() async {
    try {
      final result = await client.getData();
      debugPrint(" result: $result");
      return Resource.success(await client.getData());
    } catch (e) {
      return Resource.error('Failed to fetch datas: $e');
    }
  }

  Future<Resource<UserModel>> createUser(
      String userName, String userSurname, int userBalance, String userEmail, String userPassword) async {
    try {
      return Resource.success(await client.createUser({
        "userName": userName,
        "userSurname": userSurname,
        "userBalance": 111,
        "userEmail": userEmail,
        "userPassword": userPassword,
      }));
    } catch (e) {
      return Resource.error('Failed to create user: $e');
    }
  }

generator.dart

import 'package:dio/dio.dart' hide Headers;
import 'package:retrofit/retrofit.dart';

import '../models/user_model.dart';
import 'constants.dart';

part 'generator.g.dart';

@RestApi(baseUrl: ApiConstants.BASE_URL)
abstract class RestClient {
  factory RestClient(Dio dio, {String? baseUrl}) = _RestClient;

  @GET('/codeocean/getdata.php')
  Future<List<UserModel>> getData();

  @POST('/codeocean/adddata.php')
  @Headers(<String, dynamic>{
    "Content-Type": "application/json",
  })
  Future<UserModel> createUser(@Body() Map<String, dynamic> user);

}

adddata.php

<?php

include 'conn.php'; 

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $json_data = file_get_contents('php://input');
    $data = json_decode($json_data, true);

    $userName = $data['userName']; 
    $userSurname = $data['userSurname']; 
    $userBalance = $data['userBalance']; 
    $userEmail   = $data['userEmail']; 
    $userPassword    = $data['userPassword']; 

    $sql = "INSERT INTO users (userName, userSurname, userBalance, userEmail, userPassword)
            VALUES ('$userName', '$userSurname', '$userBalance', '$userEmail', '$userPassword')";

    if ($conn->query($sql) === TRUE) {
        $lastInsertId = $conn->insert_id;
        $response = array(
            "userId" => $lastInsertId,
            "userName" => $userName,
            "userSurname" => $userSurname,
            "userBalance" => $userBalance,
            "userEmail" => $userEmail,
            "userPassword" => $userPassword
        );
        
        echo json_encode($response);
    } else {
        $response = array(
            "status" => "error",
            "message" => "error while creating user : " . $conn->error
        );
        echo json_encode($response);
    }

    $conn->close();
} else {
    $response = array(
        "status" => "error",
        "message" => "method error"
    );
    echo json_encode($response);
}

getdata.php

<?php

include 'conn.php';

error_reporting(E_ALL);
ini_set('display_errors', 1);

$sql = "SELECT * FROM users";
$result = $conn->query($sql);

if (!$result) {
    die("Error: " . $conn->error);
}

$res = array();

while ($row = $result->fetch_assoc()) {
    $res[] = $row;
}

echo json_encode($res);

?>

user_model.dart

import 'package:json_annotation/json_annotation.dart';

part 'user_model.g.dart';


@JsonSerializable()
class UserModel {
  String? userId;
  String? userName;
  String? userSurname;
  int? userBalance;
  String? userEmail;
  String? userPassword;

  UserModel({this.userId, this.userName, this.userSurname, this.userBalance, this.userEmail, this.userPassword});

  factory UserModel.fromJson(Map<String, dynamic> json) => _$UserModelFromJson(json);
  Map<String, dynamic> toJson() => _$UserModelToJson(this);
}

I am trying to connect my flutter project to remote mysql database but I am getting error.