Flutter – FormatException: SyntaxError: Unexpected end of JSON input

I am getting this error in my flutter app during the api integration phase. I have checked the backend apis through postman they are working fine. But when i integrate it with frontend and then check it gives 404 Not Found,

 Future<Map<String, dynamic>> registerUser(
      String username, String email, String password) async {
    var baseUrl = 'http://localhost:52961/api/v1/user/';
    final url = Uri.parse('${baseUrl}register');

    _logger
        .d('Sending request to $url with email: $email, username: $username');

    try {
      var response = await http.post(url,
          body: jsonEncode({
            'username': username,
            'email': email,
            'password': password,
          }));

     ** _logger.d('Received response with status code: ${response.statusCode}');
      _logger.d('Response body: ${response.body}');**

      if (response.statusCode == 200) {
        final data = jsonDecode(response.body);
        await storage.write(key: 'accessToken', value: data['accessToken']);
        await storage.write(key: 'refreshToken', value: data['refreshToken']);
        _logger.i('User registered successfully');
        return {'statusCode': 200, 'message': 'User registered successfully'};
      } else {
        final errorData = jsonDecode(response.body);
        _logger.e('Failed to register user: ${errorData['message']}');
        return {
          'statusCode': response.statusCode,
          'message': errorData['message'] ?? 'Failed to register user'
        };
      }
    } catch (e) {
      _logger.e('An error occurred: $e');
      return {'statusCode': 500, 'message': 'An error occurred'};
    }
  }

this is my backend api code in Node.js Express. Kindly help me out because im a noob xd

i tried gpt but it tells me to check endpoints which i have for hundred times. im lost