Accessing Custom GPT (https://chat.openai.com/) using Flutter

I have created my custom GPT on https://chat.openai.com/. Now I want to write a flutter App to chat with this custom GPT. I have used chat_gpt_sdk and is able to communicate with Chat GPT. Unfortunately I am not sure how I can communicate with the Custom GPT I have created.

I used dash_chat_2 as the chat interface.

The code used to communicate with the Chat GPT server is as follows:

import 'package:chat_gpt_sdk/chat_gpt_sdk.dart';
import 'package:dash_chat_2/dash_chat_2.dart';
import 'package:flutter/material.dart';

import 'const.dart';

class Home extends StatefulWidget {
  const Home({Key? key}) : super(key: key);

  @override
  _HomeState createState() => _HomeState();
}

class _HomeState extends State<Home> {
  final openAI = OpenAI.instance.build(
    token: openai_apikey,
    baseOption: HttpSetup(// Replace with your GPT API endpoint
        ),
    enableLog: true,
  );
  ChatUser user = ChatUser(
    id: '1',
    firstName: 'Charles',
    lastName: 'Leclerc',
  );

  ChatUser gpt = ChatUser(
    id: '2',
    firstName: 'Chat',
    lastName: 'GPT',
  );

  List<ChatUser> typingUsers = <ChatUser>[];

  List<ChatMessage> messages = <ChatMessage>[];

  @override
  Widget build(BuildContext context) {
    if (messages.isEmpty) {
      messages.add(
        ChatMessage(
          text: 'Hey!',
          user: user,
          createdAt: DateTime.now(),
        ),
      );
    }
    return Scaffold(
      appBar: AppBar(
        title: const Text("Chat GPT"),
      ),
      body: DashChat(
        currentUser: user,
        typingUsers: typingUsers,
        messageOptions: const MessageOptions(
          currentUserContainerColor: Colors.black,
          containerColor: Color.fromRGBO(0, 166, 126, 1),
          textColor: Colors.white,
        ),
        onSend: (ChatMessage m) {
          getChatResponse(m);
        },
        messages: messages,
      ),
    );
  }

  Future<void> getChatResponse(ChatMessage m) async {
    m.text = m.text.trim();
    setState(() {
      messages.insert(0, m);
      typingUsers.add(gpt);
    });

    List<Messages> history = messages.reversed.map((e) {
      if (e.user == user) {
        return Messages(role: Role.user, content: e.text);
      } else {
        return Messages(role: Role.assistant, content: e.text);
      }
    }).toList();
    final request = ChatCompleteText(
      model: Gpt4ChatModel(),
      messages: history,
      maxToken: 200,
    );
    final response = await openAI.onChatCompletion(request: request);
    for (var e in response!.choices) {
      if (e.message != null) {
        setState(() {
          messages.insert(
            0,
            ChatMessage(
              user: gpt,
              createdAt: DateTime.now(),
              text: e.message!.content,
            ),
          );
        });
      }
    }
    typingUsers.remove(gpt);
  }
}

Your help is highly appreciated!