Flutter error when sending post request from API (Dio package)

I have a code where I use Dio package in flutter to post request from an API.
I checked Postman, and it returned the correct data.
The problem is:

"DioException[bad response]: The request returned an invalid status code of 405."

I used Dio package in flutter to post request from an API
When I used loginURL = "http://192.168.1.6/api/login", it ran successfully. However, when I uploaded the backend to the server and replaced the URL with something like LoginURL = "backend.com/api/login", it returned an error.

authentication.dart

Future<Map<String, dynamic>> login(String email, String password) async {
Dio dio = Dio();
try {
   final response = await dio.post(loginUrl, data: {
  'email': email,
  'password': password,
});
return {
  "success": true,
  "type": response.data['type'],
  "token": response.data["token"],
  "data": response.data
};
} on DioException catch (e) {
if (e.response != null) {
  if (e.response!.statusCode == 400) {
    return {"success": false, "message": "Invalid Credentials."};
  } else if (e.response!.statusCode == 422) {
    return {"success": false, "message": "Please Fill All fields"};
  }
}
return {"success": false, "message": e.toString()};
}
}