Unable to send the intercepted sms using REST API in flutter dart

Problem: I am trying to intercept the SMS message body and then send the message body to the database using a POST Call REST API every time I encounter an SMS. This whole interception and sending the message body should work in the background as well and that too automatically.

What I have achieved so far: I am using the telephony plugin to intercept the message body and I am able to print the message body every time I receive one at the UI level but unable to call the API and send the SMS body.

Error: Since I did not find a way to how to automatically call the API every time a new message is intercepted so I used a button to call it instead but even that did not work and it throws the error as

[error:flutter/lib/ui/ui_dart_state.cc(209)] unhandled exception: invalid argument(s) (onerror): the error handler of future.catcherror must return a value of the future's type

Also, I did not manage how do I intercept the SMS message body in the background.

To better understand this error I will be attaching a few of my code snippets:

API usage function:

String body = "";
  DateTime currentPhoneDate = DateTime.now();
  final telephony = Telephony.instance;
  interceptMessage() {
    final messaging = ApiService();
    messaging.interceptedMessage({
      "id": 50,
      "body": "$body",
      "senderName": "IDK",
      "timeStamp": "2021-10-02 12:00:55"
    })
      ..then((value) {
        if (value.status == "Success") {
          print('Message Intercepted');
        } else {
          print('Somethig went wrong');
        }
      });
  }

API Class:

Future<SmsResponse> interceptedMessage(dynamic param) async {
    var client = http.Client();

    String? token = await storage.readSecureToken('key');
    if (token == null) {
      throw Exception("No token stored in storage");
    }
    try {
      var response = await client
          .post(
            Uri.https("baseURL", "endpoint"),
            headers: <String, String>{
              'Authorization': 'Token $token',
            },
            body: param,
          )
          .timeout(Duration(seconds: TIME_CONST))
          .catchError(handleError);
      if (response.statusCode == 200) {
        print('Response Body: ${response.body}');
        final data = await jsonDecode(response.body);
        return SmsResponse.fromJson(data);
      } else if (response.statusCode == 401) {
        print("Unauthorized Request");
        return param;
      } else {
        print("Bad Input");
        return param;
      }
    } catch(e){
      print(e);
   }
  }

Telephony Plugin Usage:

 @override
  void initState() {
    super.initState();
    initPlatformState();
  }

  onMessage(
    SmsMessage message,
  ) async {
    setState(() {
      body = message.body ?? "Error reading message body.";
      print("$body");
    });
  }

  onSendStatus(SendStatus status) {
    setState(() {
      body = status == SendStatus.SENT ? "sent" : "delivered";
    });
  }

  Future<void> initPlatformState() async {
    final bool? result = await telephony.requestPhoneAndSmsPermissions;

    if (result != null && result) {
      telephony.listenIncomingSms(
        onNewMessage: onMessage,
        onBackgroundMessage: onBackgroundMessage,
        listenInBackground: true,
      );
    }
    if (!mounted) return;
  }

Handle Error Function

void handleError(error) {
    //hideLoading();
    if (error is BadRequestException) {
      var message = error.message;
      DialogHelper.showErroDialog(description: message);
    } else if (error is FetchDataException) {
      var message = error.message;
      DialogHelper.showErroDialog(description: message);
    } else if (error is ApiNotRespondingException) {
      DialogHelper.showErroDialog(
          description: 'Oops! It took longer to respond.');
    } else if (error is SocketException) {
      print(
          error); //Have to remove this part this is already being handled at the service level
    } else {
      print("All OK");
    }
  }

UI Level:

Text("$body");