Unhandled Exception: Exception: ChatGPT failed to refresh auth token: Exception: Failed to refresh access token

I created the project but in the end this error appeared for me and android studio told me it can not refresh access token this error message Unhandled Exception: Exception: ChatGPT failed to refresh auth token: Exception: Failed to refresh access token what is the solution?

this code inside chat_gpt.dart

Future<String> _refreshAccessToken() async {
  final cachedAccessToken = this._accessTokenCache['KEY_ACCESS_TOKEN'];
  if (cachedAccessToken != null) {
    return cachedAccessToken;
  }

  try {
    final res =
        await http.get(Uri.parse('$apiBaseUrl/auth/session'), headers: {
      'cookie': '__Secure-next-auth.session-token=$sessionToken',
      'user-agent': userAgent,
    });

    if (res.statusCode != 200) {
      throw Exception('Failed to refresh access token');
    }

    final accessToken = jsonDecode(res.body)['accessToken'];

    if (accessToken == null) {
      throw Exception(
          'Failed to refresh access token, token in response is null');
    }

    _accessTokenCache['KEY_ACCESS_TOKEN'] = accessToken;
    return accessToken;
  } catch (err) {
    throw Exception('ChatGPT failed to refresh auth token: $err');
  }
}

and this code is in sendMessage function

Future<ChatResponse> sendMessage(
  String message, {
  String? conversationId,
  String? parentMessageId,
}) async {
  final accessToken = await _refreshAccessToken();
  parentMessageId ??= Uuid().v4();

  final body = ConversationJSONBody(
    action: 'next',
    conversationId: conversationId,
    messages: [
      Prompt(
        content: PromptContent(contentType: 'text', parts: [message]),
        id: Uuid().v4(),
        role: 'user',
      )
    ],
    model: 'text-davinci-002-render',
    parentMessageId: parentMessageId,
  ).toJson();

  final url = '$backendApiBaseUrl/conversation';

  final response = await http.post(
    Uri.parse(url),
    headers: {
      'Authorization': 'Bearer ${accessToken}',
      'Content-Type': 'application/json',
      'user-agent': userAgent,
    },
    body: jsonEncode(body),
  );

  if (response.statusCode != 200) {
    if (response.statusCode == 429) {
      throw Exception('Rate limited');
    } else {
      throw Exception('Failed to send message');
    }
  } else if (_errorMessages.contains(response.body)) {
    throw Exception('OpenAI returned an error');
  }

  String longestLine =
      response.body.split('\n').reduce((a, b) => a.length > b.length ? a : b);

  var result = longestLine.replaceFirst('data: ', '');

  var resultJson = jsonDecode(result);

  var messageResult = ConversationResponseEvent.fromJson(resultJson);

  var lastResult = messageResult.message?.content.parts.first;

  if (lastResult == null) {
    throw Exception('No response from OpenAI');
  } else {
    return ChatResponse(
      message: lastResult,
      messageId: messageResult.message!.id,
      conversationId: messageResult.conversationId,
    );
  }
}